Engine size when using twins

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So what is it, on recreational boats is the protected keel thing just a "I have it so it is good," reason to get careless, sales and panacea gimmick or is it for real? BTW, good old Art put the keel below the props.

I think it's both. The protected prop and rudder on the typical single engine cruiser defintely offers some protection against debris and from "gentle" groundings on mud or sand bottoms.

But I'm aware of more instances of people with single engine boats (including sailboats) fouling their prop on crab pot lines or other debris than I am of people with twins doing the same thing. So this plus what I read on this forum from time to time would indicate there may be a false sense of security at play, too.

I think for the most part people with twins are very much aware of the potential vulnerability of their running gear and so take particular care to avoid hazards in the water.

We certainly do, steering around things like eelgrass and kelp mats, picking the best path through a debris-laden tide or current line, and keeping a sharp eye out at all times for things like branches, logs, lumber bits, crab and shrimp pot floats and so on.

If the light is such that it makes these things hard to see, or if we're in an area crowded with pot floats we put two peopke at the helm to better our chances of running over something.

Our boat doesn't have an autopilot anymore and this is one advantage of hand steering in waters that can have quite a bit of debris in it in that the helmsperson is always aware of what's in front of the boat because he or she can't leave the wheel and get involved in something else.

I'm not advocating not using an autopilot by any means-- most of the people we know who have and use them seem to be every bit as vigilant as we are, although we know a couple of people who have them but don't use them because they are more comfortable hand steering when there's lots of stuff in the water.

And the bottom of the keel of a GB twin is lower than the props and rudders by a fair amount which is beneficial if the boat touches ground while docked or moored during a very minus tide.
 
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I'm confident that I am not ever completely confident I will not hit something in the water... whether it is a single or twin screw boat. However, I am absolutely confident that I have better chance of missing floating debris, or semi submerged debris, and of noticing shoals while piloting from flying bridge. I try to not need to travel at night and if that need arises, I'm confident that a clear night during full moon is best... because at least some light reveals what a dark night can hide. Depending on speed a really good spotlight is useful too!
 
I also don't know when and if I am going to run my boat aground or hit a significant log, but if it happens it will most likely be because I was not properly vigilant and a protected prop may help but would not guarantee no damage or even less damage. I do agree with my twin bare props I am much more careful than I was with my many FD boats with protected props and I grounded much more often with those boats since I worried less and paid less attention. Bare props makes me a better helmsman and navigator by necessity.
 
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I run a bare prop. It does pucker you up in skinny water. When I built my boat, I made a decision that the drag of a keel and the prop induced vibes from it outweighed the benefit of the protection. My boat is dual purpose, lots of 7.5kts, but also capable of a 20kt cruise, and there the skin drag of a keel is significant.

If I ran exclusively at 7.5kts, I would have added a skeg keel.
 
I run a bare prop. It does pucker you up in skinny water. When I built my boat, I made a decision that the drag of a keel and the prop induced vibes from it outweighed the benefit of the protection. My boat is dual purpose, lots of 7.5kts, but also capable of a 20kt cruise, and there the skin drag of a keel is significant.

If I ran exclusively at 7.5kts, I would have added a skeg keel.

Representing - Planning hull being 35' lwl x 12' wlb at 20 knots:

I wonder what the additional drag coefficient really is for the following keel.

- Single, 4" thick center keel
- Tapered from 0" at stem
- 24" depth off boat bottom at skeg

Bet cha some one has a formula handy... maybe Ski or Tad! Or...??
 
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Marin thanks for the Spray update. I'd go w another color too.
In your pic it looks like the windows have been modified .. made bigger like the NT.

eyeschulman,
Just my opinion but I don't think any boat w a straight run aft is anything but a planing hull unless they have a very big keel. To get out of the planing catergory IMO it would need some rocker. Don't see it. Is the designer SD? I think he's thinking about marketing. He does that well.
 
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We've run over gillnets and long lines and never fouled the prop after 16K miles on Hobo and 40K plus miles on our sail boat. The paravanes have caught stuff though.

On our 1966 27' Chris Craft Commander (single, unprotected prop) we pulled the prop at least every year because we hit/caught something. Maybe the difference was the speed, 7 knots vs 15 plus? It wasn't for the lack of paying attention since we never ran the Chris Craft at night and no auto pilot like Marin.

Pics Hobo's bottom
 

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Greetings,
Mr. A. Double it and add 32. That'll give you a metric conversion.

That equation and a "dollar three eighty" plus tax... might get cha a cup o' java at the boat shows!
 
Marin thanks for the Spray update. I'd go w another color too.
In your pic it looks like the windows have been modified .. made bigger like the NT.

I don't know. In the black and white photo the window frames appear to be painted black or some dark color, where in the more recent photo the frames are white. This actually makes the windows in the aft cabin appear smaller.

But it's very possible things have been rebuilt some in the fifty-odd years that have ensued since Spray was launched.:)
 

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How much ??? is a dollar three eighty ? It does however make about as much since as folks on a "trawler" forum touting go fast boats. I presently own both ends of this spectrum but I am not a member of any go fast boat forums either. It does seam like the knowledge base is a lot deeper on trawler or "go slow" forums, go figure. My personal opinion is that everyone wants to be like the real trawler guys, kinda like "closet trawlering" except they're wanting folks to think they have a trawler instead of a speed boat. Apparently trawler is cooler. To me it is not a mindset or type or lifestyle, it is a "boat" that is easily indentified once you know it. It is NEVER fast, or any thing close, it cant be stepped up to beat weather, it has to be built to handle it. It doesnt slow for weather, its slow enough already. It typically has long legs, not just hunnerds of miles but thousands. It requires some form of stabilization to be habitable in any kind of sea state besides flat. Round bottom and all, kinda rolly. How many here actually own a FD trawler ? And not some speculation as to whether or not your hull really is FD or if your boat is a trawler, I mean the real thing. JMO :)
 
Marin thanks for the Spray update. I'd go w another color too.
In your pic it looks like the windows have been modified .. made bigger like the NT.

eyeschulman,
Just my opinion but I don't think any boat w a straight run aft is anything but a planing hull unless they have a very big keel. To get out of the planing catergory IMO it would need some rocker. Don't see it. Is the designer SD? I think he's thinking about marketing. He does that well.

Just some pictures of lobster boat butts. These boats are operated for the most part in SD mode and it takes very hefty power to approach planning but still no hump to jump. Yes the butt angles are flat. If my boat was done as a single it would have the same keel as pictured and a very similar hull shape. I do think the functional differences are murky and don't match the old buttock angle definitions.
 

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How much ??? is a dollar three eighty ?

Don't forget the tax! "Dollar three eighty plus tax" is an old NY slang about some low value item in a store that has no $# attached. So, when asked how much does it cost... to break the ice, you could make the funny remark... Oh, it's about a dollar three eighty plus tax. A double take is nearly always the response with a tilt of the head and the question... What did you say??? Not too unlike your question, followed by three ??? :dance: :rofl:
 
Just some pictures of lobster boat butts. These boats are operated for the most part in SD mode and it takes very hefty power to approach planning but still no hump to jump. Yes the butt angles are flat. If my boat was done as a single it would have the same keel as pictured and a very similar hull shape. I do think the functional differences are murky and don't match the old buttock angle definitions.

But everything evolves. It's like spin offs of tv shows. From Lobster boats, along came Downeast boats and they definitely aren't SD.
 
Don't forget the tax! "Dollar three eighty plus tax" is an old NY slang about some low value item in a store that has no $# attached. So, when asked how much does it cost... to break the ice, you could make the funny remark... Oh, it's about a dollar three eighty plus tax. A double take is nearly always the response with a tilt of the head and the question... What did you say??? Not too unlike your question, followed by three ??? :dance: :rofl:

Wifey B: Sure glad you clarified as I'm not old or NY so sure had no idea what it meant.

It's like the song "25 or 6 to 4."
 
Wifey B: Sure glad you clarified as I'm not old or NY so sure had no idea what it meant.

It's like the song "25 or 6 to 4".

Wifey

Didn't say I am old... just that the saying is old NY! Gran Pa Arthur taught me that one while I was in grade school. I'm 38; been holding there for couple decades! - LOL

That is a good ol' party song! I recall it well and just listened again... first time in years! :thumb:

4 am is the hour where parties get long of tooth... been there, done that... when young! :D

 
The torpedo boat is planning the blue boat is traveling in SD mode faster than hull speed but not lifting onto a stern planning surface as seen with the TB. The old buttock angle definition separating planning from SD is of little value if a boat with a flatter angle is in all other ways set up to run with most of its hull in the water in a SD mode. This is where the definitions get murky and lose a lot of their value. If the boat never gets on a full plane why call it planning not that it maters what you call it it's how it runs. The blue boat can keep that same angle of attack up to 18+k with almost full length of WL still in the water. Or do we call it full displacement planning? Or total hull distribution planning?
 

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Reminds me of the Sheriff's boat zooming past me last Saturday.
 
The torpedo boat is planning the blue boat is traveling in SD mode faster than hull speed but not lifting onto a stern planning surface as seen with the TB. The old buttock angle definition separating planning from SD is of little value if a boat with a flatter angle is in all other ways set up to run with most of its hull in the water in a SD mode. This is where the definitions get murky and lose a lot of their value. If the boat never gets on a full plane why call it planning not that it maters what you call it it's how it runs. The blue boat can keep that same angle of attack up to 18+k with almost full length of WL still in the water. Or do we call it full displacement planning? Or total hull distribution planning?

I call it "semi-planing-pretty"!

planing hull
noun, Nautical
1. a hull that tends to rise from the water when under way so that no significant amount of water is displaced beyond a certain speed.

displacement hull
noun, Nautical
1. a hull that displaces a significant volume of water when under way.

semi-displacement hull
noun, nautical
1. a hull design incorporating displacement and planing water attitudes.
2. exceeds displacement hull speed limitation.
3. below speed potential of planing hull.
 
The active word here is murky. Never thought of defining a hull type by it's angle of attack or running angle but the concept has merit. Consider a long. And slender hull w straight aft lines. A long "wheelbase" on the water and they have a tendency to run very level .. like your blue boat in the pic. And the green boat has spray rails aft to break the outbd flow from running up the sides of the hull pulling the stern down. Dosn't change the shape of the hull but changes the way it runs on the wAter.
Your Devlin boat has lots of planing hull chacteristics and quite a few ....... out of time. ....... I'm back.
FD hulls of course are usually slightly over driven but if they're not the"ll run perfectly level. For a SD or planing hull to run level it suffers huge amounts of unessessary parasitic drag w a slight reduction in wave making losses.
Most all SD hulls have some or considerable rocker that will pitch the bow up some to excessively so but when slowed down will be much more like FD hull and run much more efficiently. However the straight run hull running almost level will give a much better ride .. usually well worth the losses in efficiency.
 
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Art the SD seems to fit my boat best without using buttocks angles in the definition.

For years, my pop had a beaut of a single screw 1950, custom built sport fisher, 37' raised deck, SD hull - woody... with flying bridge. In early to mid 60's he and I restored her (PO had beat her up badly, out fishing), and, we enclosed her convertible area into a nice salon for family. Still left plenty of cockpit for fishing. Came with its original, but tired 155 hp in-line Nordberg Knight gasser. We installed 185 hp Perkins. Cruised her all over New England waters at 11 to 13 knots. WOT was 15/16 knots. Real pleasure to cruise and good in seas too. Sipped fuel. That was back when marine diesel was cheaper than gas and bellow $0.30 a gallon. I figure we were getting along at $1.00 +/- per hr at cruise. No wonder we used her so much!

Wish I had pictures. She was a doll!
 
Eye posted;
"Art the SD seems to fit my boat best without using buttocks angles in the definition."

Good observation IMO as very few hulls escape definition by the buttock lines but although that's a numerical interpetation, the numbers remains full of fuzzy definitions. All should realize definitions of P, FD and SD hulls run up and down or down and up through the three types w no hard cutoff points. The types are full of lots of variations and very fuzzy areas in between. And every element of the differences is general and foggy too. People like me like things undecided so the gray areas just offer room for thinking and discovering new ways of thinking, labeling and discussing all of the above. Those that like things decided and black and white like to close a thread .. at times early on IMO.
But many boats like mine and Marin's are obviously of one type. But planing elements and disp elements can be found in Marin's GBS. The Krogen's, Fisher's and Willard's are pure full displacement w no elements of faster hull types. Semi planing/Semi displacement hulls are by their definition word "semi" are partly this and partly that.
In the US there are those from the west and those from the east. So what is guy from Tennessee or Colorado ... It's muddy, fuzzy and semi this and semi that. OK not a great analogy ....
Eye's boat has the unmistakable look of a semi disp boat and most all would see it as such .. myself as well but from a definition standpoint it becomes hard to justify as the boat has some very strong planing hull chacteristics.
Another boat that looks like a SD design is also closer to a planing hull (actually closer than Eye's Devlin is the Camano's. They've got a very heavy and distinctive trawler .. SD look but are more shallow on the bottom and generally flatter than most planing boats. Lighter too I belive. And they are very efficient but to me they are not very SD at all.

But few look at the bottom of a boat to classify it. So the Camano's are sold, bought and operated as a trawler and semi-displacement boat .... notice I said boat and not hull.

I counterdict myself above saying there are no hard lines tween the hull types. One can get far enough into either planing or FD hull types to have a hull that no one would argue to be anything but ......
It's the semi-hulls that have grey definitions of type.
 
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I like the Racor because it is easy to do an element change without mess, elements are cheap, and a glance at the bowl confirms no water.

Don't know how you guys change spin ons without spilling fuel. A cup or ziplock helps, but that stuff is still going to run out. Then you have to fill the new one, somehow.

On my racor, I crack loose the t-handle, then pump the primer on the injection pump about 10 times. This draws down the fuel level about an inch. Pick up element and quickly into a bucket. Usually I spill nothing.

With level down an inch, I don't need to top up. Engine can handle it.

And yes, changing element can send a bit of crud on to the secondary. But that is what it is for.

I look at a set of primary spin on's, then wonder, is there any water in there?? Only way to tell is remove and dump. Messy.

I like the clear bowl.

Edit: How the heck did this post end up here?? Strange.
 
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Ski we are way off target but on a roll. Drift happens in snow and internet posts all the time. Good Racor post. I also like the big high capasity spin on fleetguard mud filters that Tony favors.
 
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When you have no specific place to be from day to day....a trip of 5 to 10 miles at 6 knots isn't all that bad.....

BAM!!!! Post of the year!!!!
 
I guess that explains why retirees love their trawlers so much.
 
Originally Posted by psneeld
When you have no specific place to be from day to day....a trip of 5 to 10 miles at 6 knots isn't all that bad.....


BAM!!!! Post of the year!!!!

True, but.... when your shortest run is 22 miles or so and most of your boating during the year is limited to weekends, an 8-knot boat well and truly sucks.
 
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Worth saying again ...


Today's run from Vallejo to Benicia/Martinez and return (exercising engine and observing/enjoying nature's and man's doings in Carqinez Strait) averaged 4-plus knots SOG against the current and eight-plus knots with, at about 1.5 gph for 6.3 knots through the water. Weather was cool, but having the pilothouse doors closed kept us comfortable. Pitied the one sailor seen in an open cockpit. ... When buddy-boating with friends, I generally leave earlier so their faster boats can catch up.


img_302287_0_be564009c36474efe06f8e403284a220.jpg
 
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