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Old 10-03-2012, 12:44 AM   #81
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Art, Marin
To get to my slip I have tI 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.
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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Old 10-03-2012, 12:58 AM   #82
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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.
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.
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Old 10-03-2012, 12:47 PM   #83
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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.
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Old 10-03-2012, 04:28 PM   #84
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Um...those who are actually using the technique don't seem to have significant issues. By the way, there's been data presented on this site for several years that demonstrate economy gains from freewheeling a prop.
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Old 10-03-2012, 08:58 PM   #85
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Um...those who are actually using the technique don't seem to have significant issues. By the way, there's been data presented on this site for several years that demonstrate economy gains from freewheeling a prop.
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
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Old 10-03-2012, 09:23 PM   #86
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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.
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Old 10-03-2012, 09:45 PM   #87
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Single Engine or twin? 36-40 Trawler.

Double your pleasure, double your fun.... Or will it?

I am interested in practical knowledge.....

Thanks

Finally closed on the sale of Windsound so my search for our new boat is on.
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.
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Old 10-03-2012, 10:41 PM   #88
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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.

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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Old 10-03-2012, 11:08 PM   #89
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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.
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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Old 10-04-2012, 08:18 AM   #90
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An economical boat is an oxymoron. It's funny how we spend so much time on ways to cut our fuel costs - is there a target? $100/year, $500, 1,000? How about don't go as far, or as fast?
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Old 10-04-2012, 08:47 AM   #91
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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.

Yes, it a slow flow rate on our boat also...throttled by the size of the small orifice on the heat exchanger tank. Since most boats have ample engine cooling, especially at lower power, it's a simple task to enlarge that bleed orifice. And easy peasy to check it all out with a Harbor Freight heat gun.

I wasn't suggesting that you cruise on one all the time given your previously stated info about the high drag characteristics of the GB 36. I was simply suggesting that free wheeling in the event of a genuine engine failure would save fuel over locking the shaft....and be more safe from the sound of your locking setup. I guess Bob Lowe let it overheat during his testing...which I aim to look up, by the way. Can't beat data for getting a handle on the real deal. And as you know the data show that the economy equation actually likes the remaining engine to run in a higher power band. So pushing up the power on the remaining engine to achieve your normal twin engine speed isn't necessarily a bad thing from the overall MPG perspective. On the other hand, the rudders on those GB look a little on the small size. Anyway, when you get your cooling lines reconfigured, you ought to give it a try...might be surprised how well it works.
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Old 10-04-2012, 08:52 AM   #92
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An economical boat is an oxymoron. It's funny how we spend so much time on ways to cut our fuel costs - is there a target? $100/year, $500, 1,000? How about don't go as far, or as fast?
Moonstruck has two 500 hp engines for a total of 1000 hp. We cruise at 25-27 knots. I won't say that fuel cost is insignificant, but it doesn't come close to the total of all the other costs. Yeah, we could run at displacement speeds or on one engine, but we didn't choose the boat for that. I am still very happy with our choice.
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Old 10-04-2012, 09:37 AM   #93
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Moonstruck has two 500 hp engines for a total of 1000 hp. We cruise at 25-27 knots. I won't say that fuel cost is insignificant, but it doesn't come close to the total of all the other costs. Yeah, we could run at displacement speeds or on one engine, but we didn't choose the boat for that. I am still very happy with our choice.
I agree

When we had our fast cruiser is was no issue to go spend $750 in fuel for a weekends boating.

We didn't switch to a larger slower boat to save fuel. We switched to gain comfort and to be able to stay onboard for longer periods of time.

I'm not running our boat on one engine either. We can throttle back to a slow cruise and get between 1.75 and 2 nmpg. Thats not bad for moving a three berdroom, two bath house around on the water.
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Old 10-04-2012, 09:59 AM   #94
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An economical boat is an oxymoron. It's funny how we spend so much time on ways to cut our fuel costs - is there a target? $100/year, $500, 1,000? How about don't go as far, or as fast?

How much an individual wants to save, and the options to get there are entirely up to each owner and I don't place a value judgement on their reasons or how they operate their boat. Understanding what is technically possible is interesting and potentially useful if it's supported by data. Discussion is virtually free.

A huge number of owners on the Great Lakes have answered your last question by tying their boats fast to the dock for entire boating season.
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Old 10-04-2012, 10:09 AM   #95
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Are folding or feathering props ever an option on these higher-powered boats, as they were on my recently departed sailboat?

Any thoughts on why folding/feathering props aren't seen on these boats? is it lack of backing ability or are there other factors? Seems like if they were viable, it would eliminate the need to freewheel. Apologies if I missed an earlier answer to this.
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Old 10-04-2012, 10:54 AM   #96
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Any thoughts on why folding/feathering props aren't seen on these boats?

They don't seen to hold up as well as a std prp.

If someone has the bucks a CPP (Controlable Pitch Prop) would be the #1 choice.

The sacrifice in the loss due to the larger diameter hub is made up for in operation.

Some folks will use a sail prop for a get home wing engine for a Blue water boat.
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Old 10-04-2012, 11:10 AM   #97
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Any thoughts on why folding/feathering props aren't seen on these boats?

They don't seen to hold up as well as a std prp.

If someone has the bucks a CPP (Controlable Pitch Prop) would be the #1 choice.

The sacrifice in the loss due to the larger diameter hub is made up for in operation.

Some folks will use a sail prop for a get home wing engine for a Blue water boat.
Thanks for the explanation. Seems like a niche there for some entrpreneur.
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Old 10-04-2012, 03:08 PM   #98
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I was simply suggesting that free wheeling in the event of a genuine engine failure would save fuel over locking the shaft....and be more safe from the sound of your locking setup. I guess Bob Lowe let it overheat during his testing...which I aim to look up, by the way.
Our current shaft locking system is great. It was the earlier system that was a bit iffy.

I don't know that Bob's boat had cooling water sent to the shaft logs. It was an Alaskan 45 (wood) with Ammaine engines. Knowing Bob I expect it did not have the shaft log cooling issue. He's not the kind of person that would deliberately allow something to overheat.
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Old 10-05-2012, 08:49 PM   #99
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Any thoughts on why folding/feathering props aren't seen on these boats? is it lack of backing ability or are there other factors? Seems like if they were viable, it would eliminate the need to freewheel. Apologies if I missed an earlier answer to this.
Other than cost, I can't think of a reason. We cruised with a Max Prop for 20 years (sail) and it was ideal for that, with no discernible (at least to me) reduction in backing ability. One nice thing about the Max Prop, at least according to the manufacturer is that as load changes, the pitch will change kinda sorta like a CPP but at a much lower cost.
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Old 10-05-2012, 08:59 PM   #100
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What about complication, potential for failure, and additional burden of maintenance cost? Are they 99.99% reliable?
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