Cross connecting the pressure line from each engine to both stuffing boxes seems like a solution to cooling. Might have to mess around with orifice size (off the heat exchangers on our boat) to get sufficient flow...
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If you could do it over again?
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Cross connecting the pressure line from each engine to both stuffing boxes seems like a solution to cooling. Might have to mess around with orifice size (off the heat exchangers on our boat) to get sufficient flow...
A HUNDRED Times a Summer!!!! Boy... that seems a bunch!!
Is that 100 different dummies on boats or simply 10 dumb-fuk "captains" having it happen 10 X each??
Only kidding! :lol:
Chip--- What did you have before you got the Sundowner Tug?
It can be. On Grand Banks boats the draft of the single engine version of a particular model is about the same as the draft of the twin engine version of the same model. Our twin-engine GB36 has the same keel as the single. However where the keel of the single stops and has the shaft tunnel, prop, and rudder shoe the keel on our boat simply reverse curves back up into the bottom of the hull.
The placement of the struts, shafts, props, and rudders of a GB twin is such that in a grounding the keel touches first. The props and rudders are actually a decent distance above the bottom of the keel. And if you really screw up and ground the boat at high tide and the boat goes over to rest on the keel and the chine as the tide goes out, the shafts, struts, props and rudders are all well clear of the seabed in the "triangle" of open space between the keel, hull, and seabed.
psneeld
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"What creates more resistance: a freewheeling propeller, or a fixed one?"
Bertram has seen conflicting data on the subject, and indeed many of you weighed in emphatically on both sides of the question. And indeed it is a bit of a trick question, because, as Ian McColgin noted, "... Like the answer to the question, "What's the best lead for a jib sheet?", the answer here is, "It depends."
First, a non-drag consideration. Some transmissions are harmed by allowing them to freewheel while the boat is moving. Not all transmission manufacturers' claims accord with boat owners' experiences on this matter, which simply tells us that many manufacturers' reps and engineers never went to sea.
The forces that contribute to prop drag when the boat is moving and the engine is off include: Resistance from the presenting surface area of the prop; turbulence behind the prop; and hydrodynamic (or aerodynamic)resistance of the prop. The first does not change much whether the prop freewheels or not. To the extent that it might diminish a little if freewheeling, the net's about the same, as there's some transmission resistance to counter. Turbulence is probably reduced somewhat if the prop is allowed to freewheel.
Dynamic resistance is nearly non-existent when the prop is held still. However, as anyone who's survived a helicopter crash can tell you, the power of a prop's autogyration is considerable. If a chopper loses power, the pilot will steepen the prop pitch a bit to get them spinning nice and fast and will then flatten the pitch to the point where they gain useful lift and are still spinning fast enough. The chopper can then be "glided" straight down.
On a sailboat with a fixed prop, the typical pitch is enough that the freewheeling prop is actually generating lots of reverse lift to resist the boat's motion. Most sailboats will experience drag from a free- wheeling prop equal to drag from a towed bucket a bit larger in diameter than the prop. The drag from a fixed prop is usually about equal to the drag from a bucket about 3/4 prop diameter if a three bladed prop and considerably less than that if two bladed.
Ian McColgin
S.V. Granuaile
A fine analysis, Ian, and it is seconded by this month's winner, Commander David E. Davis, USN. He writes:
Sorry but...it depends. According to the U.S. Navy Towing Manual, Appendix H, when you determine the strain for a towed vessel the propeller resistance is a function of the projected waterplane area of the prop, times a constant (3.737), times the velocity of the tow squared.
So the faster you tow, the faster the prop resistance increases. For example: for a typical destroyer the towing resistance attributed to the prop(s) at 6 knots is 34k pounds while at 8 knots the same prop(s) yields 61k pounds. This is based on a fixed controllable reversible pitch wheel. A controllable reversible pitch prop would be set max ahead to minimize resistance. But then some ships save fuel when steaming independently at higher speeds by simply trailing a freewheeling prop. This discounts any concerns re shaft seals, machinery lubrication, etc..
The bottom line is that there is likely a crossover velocity where the resistance of a fixed prop (braking effect) becomes greater than the force required to impart rotation to the entire gear train (in a freewheeling prop), but studies on the topic are scarce. Given the small waterplane area of most sailing vessel's props, the relatively slow speed through the water, and the overriding desire to minimize wear on the shaft seal and transmission, fixed is the way I'd go (at max ahead or better, feathered, if the pitch is variable).
CDR D.E. Davis, USN
Commanding Officer, Naval Diving and Salvage Training Center
I don't know...too much conflicting data and one study from MIT who makes money from publishing reports....just don't know....not that it probably matters worth a hill of beans for most of us
Bertram has seen conflicting data on the subject, and indeed many of you weighed in emphatically on both sides of the question. And indeed it is a bit of a trick question, because, as Ian McColgin noted, "... Like the answer to the question, "What's the best lead for a jib sheet?", the answer here is, "It depends."
First, a non-drag consideration. Some transmissions are harmed by allowing them to freewheel while the boat is moving. Not all transmission manufacturers' claims accord with boat owners' experiences on this matter, which simply tells us that many manufacturers' reps and engineers never went to sea.
The forces that contribute to prop drag when the boat is moving and the engine is off include: Resistance from the presenting surface area of the prop; turbulence behind the prop; and hydrodynamic (or aerodynamic)resistance of the prop. The first does not change much whether the prop freewheels or not. To the extent that it might diminish a little if freewheeling, the net's about the same, as there's some transmission resistance to counter. Turbulence is probably reduced somewhat if the prop is allowed to freewheel.
Dynamic resistance is nearly non-existent when the prop is held still. However, as anyone who's survived a helicopter crash can tell you, the power of a prop's autogyration is considerable. If a chopper loses power, the pilot will steepen the prop pitch a bit to get them spinning nice and fast and will then flatten the pitch to the point where they gain useful lift and are still spinning fast enough. The chopper can then be "glided" straight down.
On a sailboat with a fixed prop, the typical pitch is enough that the freewheeling prop is actually generating lots of reverse lift to resist the boat's motion. Most sailboats will experience drag from a free- wheeling prop equal to drag from a towed bucket a bit larger in diameter than the prop. The drag from a fixed prop is usually about equal to the drag from a bucket about 3/4 prop diameter if a three bladed prop and considerably less than that if two bladed.
Ian McColgin
S.V. Granuaile
A fine analysis, Ian, and it is seconded by this month's winner, Commander David E. Davis, USN. He writes:
Sorry but...it depends. According to the U.S. Navy Towing Manual, Appendix H, when you determine the strain for a towed vessel the propeller resistance is a function of the projected waterplane area of the prop, times a constant (3.737), times the velocity of the tow squared.
So the faster you tow, the faster the prop resistance increases. For example: for a typical destroyer the towing resistance attributed to the prop(s) at 6 knots is 34k pounds while at 8 knots the same prop(s) yields 61k pounds. This is based on a fixed controllable reversible pitch wheel. A controllable reversible pitch prop would be set max ahead to minimize resistance. But then some ships save fuel when steaming independently at higher speeds by simply trailing a freewheeling prop. This discounts any concerns re shaft seals, machinery lubrication, etc..
The bottom line is that there is likely a crossover velocity where the resistance of a fixed prop (braking effect) becomes greater than the force required to impart rotation to the entire gear train (in a freewheeling prop), but studies on the topic are scarce. Given the small waterplane area of most sailing vessel's props, the relatively slow speed through the water, and the overriding desire to minimize wear on the shaft seal and transmission, fixed is the way I'd go (at max ahead or better, feathered, if the pitch is variable).
CDR D.E. Davis, USN
Commanding Officer, Naval Diving and Salvage Training Center
I don't know...too much conflicting data and one study from MIT who makes money from publishing reports....just don't know....not that it probably matters worth a hill of beans for most of us
The mistake some people make in this "freewheel vs locked" issue is trying to equate an air propeller (helicopter, plane) to a water propeller. An air propeller has very little surface relative to the entire propeller disk. A water prop may cover the entire propeller disk or if not, certainly most of it.
This is why a stationary propeller moved through the water creates way more turbulence and thus drag in proportion to a stationary air prop moved through the air.
This is why a stationary propeller moved through the water creates way more turbulence and thus drag in proportion to a stationary air prop moved through the air.
Really - That's a great design feature. Therefore, if desired, on a relatively firm sea bed (not too mushy/muddy) the GB twin screw could have one or the other of its bottom's sides (inc. prop, rudder, shaft, strut...etc...) tended to (i.e. worked on) without hauling in areas with sufficient tide level change. For emergency purposes that might come in handy. In Maine we did similar with old woody Lobster boats, but they were single screw. Just gotta make sure all is lashed down on decks and inside - angle gets fairly steep. I wonder how many other boat designs afford a sufficient "triangle" of open space, such as GB - - > I can assure you Tollycrafts do not. At least not ours or any other Tolly I’ve seen. But, then again our boat’s bottom is planned for speed. When it comes to going aground in a Tolly... YOU JUST DON"T!!!
Attached is a pict of a 40’ Tolly that hit the beach at some 12 knots, I believe near your stomping groungs... err floating waters!. Old folks had her on AP and the beforehand party had been severe, I guess... so all were asleep. That’s one way to clean off the barnacles!
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Art, Marin
To get to my slip I have to pass the lifter at our marina. There I have seen a variety of boats lifter out of the water, with their stern towards me, including the GBs Marin describes and the Tollys like Art's. I have also seen many GBs, more than those like Marin's, that have a shallow keel like Art's picture of a Tolly, with the bottom 1/2 of both props hanging below the depth of the keel.
So if you have a GB, know your own boat, don't assume it is as described by Marin.
To get to my slip I have to pass the lifter at our marina. There I have seen a variety of boats lifter out of the water, with their stern towards me, including the GBs Marin describes and the Tollys like Art's. I have also seen many GBs, more than those like Marin's, that have a shallow keel like Art's picture of a Tolly, with the bottom 1/2 of both props hanging below the depth of the keel.
So if you have a GB, know your own boat, don't assume it is as described by Marin.
Moonstruck
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Many of the later model Grandbanks have a modified V hull with an abbreviated keel and propeller pockets. This reduces draft, but the props have more exposure. Some of their new hulls have POD drives. They are fast boats if enough power is supplied.
Giggitoni
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"... this month's winner, Commander David E. Davis, USN. writes:
Sorry but...it depends. According to the U.S. Navy Towing Manual, Appendix H, when you determine the strain for a towed vessel the propeller resistance is a function of the projected waterplane area of the prop, times a constant (3.737), times the velocity of the tow squared.
So the faster you tow, the faster the prop resistance increases. For example: for a typical destroyer the towing resistance attributed to the prop(s) at 6 knots is 34k pounds while at 8 knots the same prop(s) yields 61k pounds.
In an offhand way... the above description/formula reminds me of a problem when approaching the speed of light... eventually the mass doing so becomes infinite! Or, for layman terms in regard to the prop drag on boats moving in the range of 3 to 12 knots with a freewheel or static prop, i.e. any number of our boats on TF: “Angle of the dangle is directly proportionate to hypotenuse of the square”. In other words - Although this gives us all plenty to chat about and learn from - - > It ain't No Big Deal in the long or short run! :lol:
Anode
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Marin - The last boat we had was a S-2 9.2C sailboat.
We started out looking for something in the 40 for range. Motorsailer or trawler type. Kids are grown so it's just the wife and I. We don't do social very well. Especially on a boat. Both of us have had enough people interaction in our professional lives.
First saw my first Sundowner Tug in Anacortes and tried to buy it as we felt it had enough room in it to do everything we needed.
Finally found one on the Ohio River. Bought it and brought it home. The rest is history.
I have spent lots of time on both sail and power boats in the 40 -50 foot range. Singles and twins, fast and slow. Speed is not an issue. I'm a sailor at heart. Julie is into slow too.
Scout has a single Kubota engine (500 hrs) that cruises at 6.7 knots @ 2000 and burns about a gallon of fuel an hour. I have not had issues handling the boat with a single engine either with my wife or single hand. It has a low profile with a 10 foot air draft. Water draft is less than 3 feet.
Head, sanitary lines, Electra Scan all new. All thru-hulls and seacocks new. Electrical new. Auto pilot new. Refrigerator and freezer new. Drive line bearings, cutlass bearings and flex stern tube new. Rudder bearing and packing assembly new, GPS/radar new, genset 3 hrs almost new, windows new, 3000 watt true-sine inverter new, bottom stripped to glass and epoxy coated, AC/Heatpump...you get the picture.
We now have a very comfortable (for two people) 30 foot boat with a 12 foot beam. It can be moved by trailer w/o removing any 'body parts' under a wide load permit. It does not have a separate shower which I would have preferred but we did add a cockpit shower that works great. We have no intention of selling out and being liveaboards but the loop is in our future. A few weeks on the boat and a few weeks at home.
We have only had Scout in the water for a couple of months but still feel it's the perfect boat for us.
I'm 65 and hopefully have done my last major boat project. Time to enjoy.
Well, maybe. The boat will lean over and sit like that but the question is what happens when the tide comes back in. Lots of variables here, of course, but it's not uncommon for the water level to rise above the level of the deck on the down side before the boat will start to float and right itself. Which means that water can flow into vents or under doors or down through hatches and flood the boat which means it will never right itself. It will just sit there on the bottom while the water rises around it.
I don't know if a GB is in this category or not. I know of a GB42 woody that went aground on a notorious mud flat south of Anacortes. I've seen photos of it sitting on the mud and it sat as I described in my previous post. But when the tide came back the boat did not float and right itself before the water could start entering the boat. According to the person who salvaged the boat and subsequently rebuilt it, it was basically sunk although it did not disappear from sight.
But GB woodies and the first few years of fiberglass GBs have their engine room air intakes on the outsides of the bulwarks. So unless you can seal them up really well, I imagine an incoming tide would start flooding the boat before it started to float. Don't know what the situation is on later GBs.
Tom.B
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But would y'all have done it differently? 
I love our single Perkins. It was perfect to learn all about diesels. I was new to them and had a panic attack when I saw the engine room of a SeaRay we almost bought that had 2x3208's. If I did it again and know what I know now? I would get twins and be able to hit 12-ish knots. Or perhaps one bigger single.
That's all.
I love our single Perkins. It was perfect to learn all about diesels. I was new to them and had a panic attack when I saw the engine room of a SeaRay we almost bought that had 2x3208's. If I did it again and know what I know now? I would get twins and be able to hit 12-ish knots. Or perhaps one bigger single.
That's all.
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Giggitoni
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The engine room air intakes on our 1986 GB42 are on the sides of the cabin about one foot above the deck. So I guess it's possible that rising water could re-float the boat without it sinking.
But would y'all have done it differently?
Had we known then what we know now we may have gotten a GB36 Europa instead of a GB36 Classic (tri-cabin). For just two people the Europa is a more user-friendly boat in some ways in this climate where it rains all the time (except for right now) and is often windy and cold. The Europa's covered aft deck which can be enclosed and even heated makes for a great living space in which you can be outdoors without being outdoors.
The downside of the Europa in a smaller boat like the GB36 is that there is only one stateroom, in the bow. So if you have guests somebody has to sleep in the main cabin on a berth converted from the settee. Which means the berth has to be made up every evening and stowed in the morning. Plus there is only one head.
With the Classic there is the aft stateroom and the forward stateroom (V-berth), each with its own head, with the main cabin as neutral ground between them. So people can get up and make coffee or whatever, go outside for a walk, etc. without disturbing the people in the other stateroom.
Had we decided to get a larger boat 14 years ago we would definitely have gone with a Europa with two forward staterooms. Or a pilothouse boat, still in the Europa configuration.
BruceK
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For a couple, our IG36 Europa works well. The only dedicated berth in the bow is semi island, but we can make up a decent double in the saloon. Shower and head are separate compartments.Both saloon and cockpit are a good size. Clears cutoffs across the walkways at the end of the saloon, plus full mesh covers and the extended flybridge keep the cockpit fairly dry in rain.
We were recently shown over a TF members IG36 with 3 dedicated sleeping cabins plus saloon; it would definitely suit a family far better than our "selfish couple" layout. BruceK
Chip - That's as close to perfect for two lovers as any easy to handle boat I've heard of. Good Job!
Art
markpierce
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I'm a "sleep two, feed four, entertain up to six (including self)" kind of guy. With four or more people staying overnight, one really needs at least two heads which I don't have. Two heads are twice the headache. Much too crowded in a mid-30-foot boat. Exception, feeding five here and in a pinch six, but we brought the meal from ashore.
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GB changed their hull design in the 2000s for their newer models, the GB44 which later became by virtue of a different way of measuring the boat the GB47, and the GB41 which is the pod-drive model. These hulls are very different than the original GB hull.
The Kenneth Smith hull and keel configuration I described earlier was used on all GBs from the first GB36 woody in 1966 up through the end of each model's fiberglass production. So the GB32, 36, 42, 46, 49, and 52. Of these, the only one still in production is the GB52.
The twin engine GBs of these models all have keel, shaft, prop, and rudder configurations like the one pictured by Giggitoni. Bellingham has a large GB charter/sales operator and I see all manner of GBs in the Seaview Yard year round. I have never seen any of the so-called classic models with a shallow keel. The twins all have keels like our boat (and Giggitoni's), and the singles have the same keel but with the aft end squared off to incorporate the prop and rudder shoe.
While there is a GB47 in the charter fleet I have not yet seen a GB44/47 or GB41 out of the water. But I've seen plans of their hulls and they look nothing like the GB classics.
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Of course the huge advantage you and your wife have over most other boat owners is that you know every inch of your boat and every detail of its systems. I suspect there will be very few times--- if any--- when the boat will "take you by surprise" and cough up a problem you can't diagnose almost instantly. It is an enviable position to be in, in my opinion, and is one reason my wife and I try to do as much on our boat ourselves as we can.
Nomad Willy
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This issue has been discussed in greater depth on BoatDesign.net. I was surprised to accept the consensus that a twin running slow on one engine is definitely considerably more fuel efficient than running slow on both engines. Even w the prop of the off engine dragging through the water. The reason for this is the very large heat loss per hp of an engine running at very low loads. And w two doing this the heat loss through the cylinder walls and piston and combustion chamber is absolutely enormous. But w only one engine running at a bit over twice the load the heat loss is more than halved. Big savings ... enough to overcome the loss of the drag of the dead prop and the asymmetrical thrust loss and still come out w a bit of a gain.
Re some of the negative elements Marin mentions and others I couldn't see myself doing it unless I was desperate to reduce fuel burn. And if one has a big yacht and he hasn't got money for fuel I'm convinced he has the wrong boat. In the past fuel prices have gone up and come back down. I don't see that happening to any significant degree any more so I think those running single on a twin need to get a more suitable boat before things get worse. $3.00 a gallon gas is probably never to happen again. Buck up and take appropriate action is my take on this. BUT running single does save considerable fuel.
Re some of the negative elements Marin mentions and others I couldn't see myself doing it unless I was desperate to reduce fuel burn. And if one has a big yacht and he hasn't got money for fuel I'm convinced he has the wrong boat. In the past fuel prices have gone up and come back down. I don't see that happening to any significant degree any more so I think those running single on a twin need to get a more suitable boat before things get worse. $3.00 a gallon gas is probably never to happen again. Buck up and take appropriate action is my take on this. BUT running single does save considerable fuel.
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BruceK
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Even so,the amount of water force exerted on a prop/shaft/gearbox not being engine driven must be considerable.A charter ferry which could not start its engine conventionally used to get towed, gear in neutral,and put into gear, to turn and start the engine. Similar to rolling a manual/stick shift gearbox car with a flat battery downhill, putting it into gear with ignition on, dropping the clutch,to start the engine.BruceK
Not long after getting our boat we wanted to find out how long it takes the shaft to stop rotating when pulled out of gear at idle rpm and at cruising speed. We particularly wanted to know how long it took for the shaft to stop rotating at idle power so we'd know how long to pause in neutral when shifting between forward and reverse. So we opened the main cabin hatch to the engine room and watched.
At cruising speed (8 knots) when the power was reduced to idle and the shifters pulled to neutral the shafts continued to be driven by the boat's forward motion until the boat had almost come to a complete stop. And the speed of rotation as the boat slowed down appeared to be the same as it would have been turning had it been pushing the boat at that speed, although we did not actually measure this.
The freewheeling rpm will be affected by the friction in the driveline, of course. But the turning force applied to the prop as the boat moves through the water is considerable.
This has really been driven home when we've had to tie off a shaft. The pressure on the line preventing the shaft from rotating is impressive, to say the least. Guitar-string-tight would not be an overly dramatic description. After realizing how high the rotational pressure is I fabricated tie-down brackets and mounted them to the underside of the main cabin floor beams directly over the shaft couplers. They are heavily screwed and 5200'd to the beams and provide strong points to secure the line locking the shaft should we have to shut an engine down.
At cruising speed (8 knots) when the power was reduced to idle and the shifters pulled to neutral the shafts continued to be driven by the boat's forward motion until the boat had almost come to a complete stop. And the speed of rotation as the boat slowed down appeared to be the same as it would have been turning had it been pushing the boat at that speed, although we did not actually measure this.
The freewheeling rpm will be affected by the friction in the driveline, of course. But the turning force applied to the prop as the boat moves through the water is considerable.
This has really been driven home when we've had to tie off a shaft. The pressure on the line preventing the shaft from rotating is impressive, to say the least. Guitar-string-tight would not be an overly dramatic description. After realizing how high the rotational pressure is I fabricated tie-down brackets and mounted them to the underside of the main cabin floor beams directly over the shaft couplers. They are heavily screwed and 5200'd to the beams and provide strong points to secure the line locking the shaft should we have to shut an engine down.
Delfin
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As noted, the debate over single vs twins has been rather thoroughly hashed out. Delfin is a single, but has a bow and stern thruster. IMHO, the stern thruster provides superior maneuvering capable as compared to twins, so the argument of greater maneuverability doesn't make a lot of sense, at least to me.
Double your pleasure, double your maintenance costs.
As mentioned earlier, a cross connection for the cooling water would address the stuffing box cooling and free wheeling the prop would likely save you fuel during the trip home.
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The cooling water pickoffs on the FL120 supply just barely enough water for one shaft log. Splitting it would invite overheating of both shaft logs.
Also, as was demonstrated and charted by Bob Lowe on the GB owners forum the fuel savings in a boat like ours even with the unpowered prop freewheeling would be minimal to none, depending on the power setting.
As to deliberately running on one to save fuel, while fuel is certainly getting more expensive, compared to all the other costs associated with boating it's still practically free. It's certainly not expensive enough yet to make it worth slowing our glacial 8-knot pace through the water even more just to save a few bucks per trip.
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