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Old 04-05-2015, 04:25 AM   #1
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Which hull material ?

It seam we got a Customer for our actual "passagemaker"

( "Passagemaker" cherchez l'erreur ! - Trawler long-cours )

We project to built an evolution from Hoa, near similar hull but different superstructures, because a colleague want also built an evolution of Hoa and the easiest way is to built two similar boat ( in reality two similar hull and some differences inside) normally after discussion it will be the N6 on this page, the last one .

Un Compromis, oui mais lequel !? - Trawler long-cours

Normaly we project to built the hull in alloy like Hoa... but a boatyard contact us and propose to built her in "composite" (sandwich epoxy resin, fiber glass , Kevlar and foam ) in this case we could "save" 3,5 t ) in the hull weight ...yes but ?
Your filling , your experience , your practice with this material ?

Thanks !

And you witch profile did you prefer ?
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Old 04-05-2015, 06:11 AM   #2
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Quote:
Originally Posted by longcours62 View Post
It seam we got a Customer for our actual "passagemaker"

( "Passagemaker" cherchez l'erreur ! - Trawler long-cours )

We project to built an evolution from Hoa, near similar hull but different superstructures, because a colleague want also built an evolution of Hoa and the easiest way is to built two similar boat ( in reality two similar hull and some differences inside) normally after discussion it will be the N6 on this page, the last one .

Un Compromis, oui mais lequel !? - Trawler long-cours

Normaly we project to built the hull in alloy like Hoa... but a boatyard contact us and propose to built her in "composite" (sandwich epoxy resin, fiber glass , Kevlar and foam ) in this case we could "save" 3,5 t ) in the hull weight ...yes but ?
Your filling , your experience , your practice with this material ?

Thanks !

And you witch profile did you prefer ?
Nice boat!

Normally speaking the lightest building material that's affordable is plywood, then alloy and of course steel. This looks like a displ. Hull, so weight doesn't make much difference to the performance.

Rather than alloy (more than twice as expensive), and GRP for a one off (even more expensive) I'd go for steel.

Cheap.
Easy to repair anywhere in the world.
Epoxy paints cure rust problems.


.... a 66' hull in alloy would probably cost about 150k to fabricate, or about 70k in steel.


That's a big saving.
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Old 04-05-2015, 08:17 AM   #3
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Steel could be

Rather than alloy (more than twice as expensive), and GRP for a one off (even more expensive) I'd go for steel.

Cheap.
Easy to repair anywhere in the world.
Epoxy paints cure rust problems.


.... a 66' hull in alloy would probably cost about 150k to fabricate, or about 70k in steel.


That's a big saving.[/QUOTE]



We also thinking steel but for example just if the hull will be made in steel rather than aluminium it means 9 tonnes heavier. more cost in paint (but I agree with you ,with perfect initial sand blasting and paint job, it could be good for decades)
In alloy around 33T full displacement
In steel 42 T
In "composite" 29T
For example in steel it means around 30% more hp at 10 kts than alloy and 23% more at 8 kts.
More paint , diesel , less material cost ????
20 years ago when we prepare the built of our actual passagemaker we already try to make this comparaison finally we decide go to aluminium and now again we must make a choice
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Old 04-05-2015, 09:00 AM   #4
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Originally Posted by longcours62 View Post
Rather than alloy (more than twice as expensive), and GRP for a one off (even more expensive) I'd go for steel.

Cheap.
Easy to repair anywhere in the world.
Epoxy paints cure rust problems.


.... a 66' hull in alloy would probably cost about 150k to fabricate, or about 70k in steel.


That's a big saving.


We also thinking steel but for example just if the hull will be made in steel rather than aluminium it means 9 tonnes heavier. more cost in paint (but I agree with you ,with perfect initial sand blasting and paint job, it could be good for decades)
In alloy around 33T full displacement
In steel 42 T
In "composite" 29T
For example in steel it means around 30% more hp at 10 kts than alloy and 23% more at 8 kts.
More paint , diesel , less material cost ????
20 years ago when we prepare the built of our actual passagemaker we already try to make this comparaison finally we decide go to aluminium and now again we must make a choice
[/QUOTE]

33tons at 5hp/ton isn't that much different to 42tons at 5hp/ton needed to Chug along at displ. Speed.

Call it 10 tons more that needs an extra 50hp at 20hp/gal diesel engine output.

The extra cost of a steel boat would be about 2 1/2 gals hr over its lifetime.

How long does it take to burn 80k of diesel a steel hull saves?
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Old 04-05-2015, 09:09 AM   #5
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Greetings,
Mr. RB. I agree, one can buy a LOT of diesel for 80K BUT that 60 gallons per day (2.5 gph X 24hrs) will allow some greater range IF fuel stops are few and far between.
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Old 04-05-2015, 09:58 AM   #6
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Materials of construction are one thing, build quality and design quite another. Pick a yard that can point to what their previous builds are and go examine them, closely. Better yet, take along an experienced builder /designer who knows the pitfalls of boat construction and design.
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Old 04-05-2015, 10:42 AM   #7
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Rustybarge wrote in post #2;
"Normally speaking the lightest building material that's affordable is plywood, then alloy and of course steel. This looks like a displ. Hull, so weight doesn't make much difference to the performance."

Not so at all. Weight is very much a function of performance in a FD hulled boat. To calculate how much power will be required to drive a FD boat weight is most often used for typical hulls .. 4 or 5hp per ton of disp. It's more or less directionally proportional. twenty five percent less weight = 25% less power required. Where it's not directionally proportional is in the matter of speed. That's controlled mostly by the hull, it's size and weight.

A 36' GB (because it's typical) w two big heavy engines, heavy ground tackle, a big heavy dinghy will suffer (performance wise) a great deal compared to it's opposite .. a GB w light engines, a combination rode and a reasonably light dinghy. And the owner w heavy engines, heavy dinghy and heavy ground tackle will be strongly inclined to bring aboard lots of other stuff that's heavy .. those w an opinion like Rustybarge (and my father) I'd say. So there's a wide range of total weight that a GB 36 would typically weigh. There could be GBs out there weighing 25% less than others. And those boats will have 25% better performance. So I say no .. weight is very much a function of performance for FD trawler type boats.

And of course weight (or lack of it) would be even more important w a SD hull. Rustybarge is spot on re plywood but I'm baffled why no mention of FG in that paragraph.
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Old 04-05-2015, 11:20 AM   #8
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Quote:
Originally Posted by manyboats View Post

A 36' GB (because it's typical) w two big heavy engines, heavy ground tackle, a big heavy dinghy will suffer (performance wise) a great deal compared to it's opposite .. a GB w light engines, a combination rode and a reasonably light dinghy.
Not true. Or not true to the point it matters. We first chartered a 1991 GB36 single engine, no generator, small, light inflatable dinghy before buying our own 1973 GB36. The charter boat had minimal "belongings" on board. Ours is a twin with a big generator, two heavy-ish fiberglass dinghies on board and a hull construction that is much heavier than the later boat. And we have all kinds of "belongings" on board.

Our boat weighs 30,000 pounds on the Travelift. The charter boat weighed about 26,000 pounds.

And the efficiency of boath boats in terms of speed and fuel consumption is almost the same. The single-engined boat burns a little less fuel per hour but not half because that one engine has to burn more than each of the engines in our twin. Plus the single has a bigger engine, 220 hp Cummins vs. 120 hp FL120.

We run our two engines at 1650 rpm. Cruise rpm of the single is 2,000 rpm. Speed through the water in both cases is 8 knots. Our total fuel consumption is about 5 gph. The single is about 3 gph.
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Old 04-05-2015, 02:28 PM   #9
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For similar hull form

The difference of weight :
30 T in composite
33 T in alloy
42 T in steel

you can read on the files the difference is significant .
And it is not a difference of 80k but 80 k less sand blasting and painting, less some stainless steel part .
But the 42 T steel would have a D/L ratio of 160

our actual alloy boat D/L 155 nit so big difference for this ratio but in case of composite hull it could be ...114
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Old 04-05-2015, 04:48 PM   #10
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Composite hull advantages

My only experience with composite hulls has been with racing sailboats. There is no question lb for lb they are much stronger than other hull materials. One of the advantages of light building material is being keep the ends of the boat light centralizing weight which reduces the pendulum effect which improves the ride and make a boat more easily driven in waves. I also think it is possible make make more complex hull shapes with composite. Having light ends also put less structural loads on a boat. I think there is a lot to learned from racing sailboats when it comes to efficient hull shapes and construction. Sailboats have been working on driving boats though the water with limited hp for years, almost all high speed sailboats today use composite construction, even masts and booms.
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