Aluminium boat building - 25ft fisherman

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fallguy1000
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Re: Aluminium boat building - 25ft fisherman

Post by fallguy1000 »

fyi-not to be a nit, but that GW has two strakes, one is hidden by the port ducer.
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cracked_ribs
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Re: Aluminium boat building - 25ft fisherman

Post by cracked_ribs »

Honestly...none of this needs to be very complicated.

If the stringers are going to be like a typical cs25, space the strakes out a bit on either side of the stringers. You don't want the headaches of welds on top of welds, and you do want the extra stiffness from the strakes to help you where the hull is floppiest.

If you're doing lots of smaller lengthwise stiffeners instead of a typical glass boat with two or four big stringers, just space them about thirds apart on the hull.
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fallguy1000
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Re: Aluminium boat building - 25ft fisherman

Post by fallguy1000 »

cracked_ribs wrote: Fri Jul 23, 2021 9:31 am Honestly...none of this needs to be very complicated.

If the stringers are going to be like a typical cs25, space the strakes out a bit on either side of the stringers. You don't want the headaches of welds on top of welds, and you do want the extra stiffness from the strakes to help you where the hull is floppiest.

If you're doing lots of smaller lengthwise stiffeners instead of a typical glass boat with two or four big stringers, just space them about thirds apart on the hull.
I agree. I don't know stringer locations, but I'd go inside them if they are farther apart and then outside again same or so. You may lose the outer strake at speed, big deal.

So, for example, something like stringers 2' from centerline, first strake ends at 18", second at 30", allows for bunking trailer, if desired, from 21-27" with 3" margin.
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fallguy1000
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Re: Aluminium boat building - 25ft fisherman

Post by fallguy1000 »

The outside one in my example is open for debate. Might be getting near the chine and that can get wonky...
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cracked_ribs
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Re: Aluminium boat building - 25ft fisherman

Post by cracked_ribs »

Yeah...sometimes this stuff is easier to draw than explain so here's a sketch that I hope covers what I'm describing:

Image

The strakes do a couple of things, they make it plane a little easier, and they make the bottom a little stiffer, and they also give you a bit of grip while cornering.

In glass boats you really need the shape to stiffen up the hull, that's why they're always there. If you do typical CS25 stringers like the top drawing I'd want them there for stiffness as well.

If you do longitudinal stiffeners like the bottom drawing you won't likely need the stiffening effect, but the grip in corners is still nice.

Getting on plane easier is also good...but everything you do that makes it easier to plane a given hull, also makes the ride rougher.

Anyway not a huge deal, either way. You probably won't be running with the top strake exposed, I rarely see that on anything but purpose-built go-fast boats. And if you are, you probably won't be cranking hard on the wheel and cornering like crazy. I think often people overthink this stuff. Just stay away from where the stringers are going to go, and you will get the extra stiffening if you need it.


Plus you will probably have an easier time with heat distortion etc. Not that I'm a great welder or anything; I can weld but not enough to attempt a project like this, so you're already better at it than I am. But that's what I would do.
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TomW1
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Re: Aluminium boat building - 25ft fisherman

Post by TomW1 »

Excellent drawings CR. Now we only need to know where he is putting his stringers and calculating how wide his strakes need to be. You did not mention it but they also help getting up on plane faster. Agree with you on the ride that is why you have to make a compromise between between lift and ride when you design them.

Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

lucastefanel
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Re: Aluminium boat building - 25ft fisherman

Post by lucastefanel »

Hi guys, sorry I've been out of forum for a long time but material went 3 times more expensive than normal price so I quitted activities for some months.
Anyway, I made some good progress on my boat.
First of all I did not installed strakes yet, I focused my efforts on giving a shape of real boat but now or later I will have to decide how to proceed ons strakes.
Here below some pictures on how is boat now.
Lot of works still to do but I'm studying every day how to go ahead in order to put her in the water by beginning of next spring.
I'm proceeding now on cabin structure (actually you can note also the bed), hopefully next week I'll be able to start consolle installation.
Slowly slowly is getting the right shape, of course I'm so far from target but never give up!!
Of course Every suggestion or critic is welcome!

Cheers!!
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Fuzz
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Re: Aluminium boat building - 25ft fisherman

Post by Fuzz »

That is going to be a very nice looking boat!

TomW1
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Re: Aluminium boat building - 25ft fisherman

Post by TomW1 »

Wow, things have really come along. Nice work and like Fuzz that is going to be a nice looking boat. Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

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