TX18 Foam core stringers, ribs and sole. Strakes.

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Vundu
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TX18 Foam core stringers, ribs and sole. Strakes.

Post by Vundu »

Hi Guys,
I am not sure if this is the right place to voice these questions as they cover foam core materials and some design advice. Appologies in advance if this is incorrectly placed. So.. here goes.
History:
A couple of years ago I placed a question about building a TX 18 using foam core, with the advice recieved I opted to build with ply as no one was in a position to give me a definite laminating schedule. This went well, and now I would like to build another, but with some mods.

1) I am going to go up to 115hp Merc, which is +-90lbs heavier than the recomended 60hp max. Reason being this is what I already have.
2) lift the sole to allow for some under floor storage (4- 6 inches).
3) Raise the sheer (4-6 inches).
4) Increasing the hull size by 7% in all aspects, (as that keeps the beam within our trailering width laws).

My foam core questions are:
1) Can I build the stringers, ribs and sole out of a foam core material, keeping the rest of the hull ply. The stringers and ribs would be deeper than currently designed (to allow for storage) and therefore stronger??. If yes, is there any advice what the laminating schedules should be and core material used?

Non foam core question.
I would think that with such a flat bottomed hull a main reason not to increase HP is the posibility of a blow out on a sharp turn. Would adding a single or a pair of strakes have a potential benefit?

Thanks very much for taking the time to read this.



jacquesmm
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Re: TX18 Foam core stringers, ribs and sole. Strakes.

Post by jacquesmm »

I am glad to hear that you like your TX18 but can we have a performance report and some pictures?

Some of your questions are easy to answer, others not.
Let's start with the easy ones.

Scale by 7%: no problem at all.

Raise the sides 4 to 6" easy, you can do that.
BTW, we can talk metric, 10 to 15 cm is fine.

Raise sole for storage: yes, as long as all the framing is present and is raised the same way.

More HP: not ideal but the transom can take it. Trim at rest may not be nice but it is possible. We will have to move tank and battery for the CG.

Foam core: no problem at all if you make the bottom from plywood epoxy. All other parts can be made in foam sandwich and I can give specs.
I can give specs for the bottom too but I will consider them experimental. You may have seen the debate about the PH22 in foam. The TX18 does not slam as much as a low deadrise and with the proper foam and resin, there will be less risk of shear failure than with the PH22.
Your problem is one of supplies: how easy is it to get supplies in Zambia? BBC can ship in a container, we have done it a few times.

Strakes: I don't like that idea. You know that the boat hull shape is based on the Hickman's sled. Hickman and others designed many hulls in that style and in some cases, there was a problem with chine tripping. For that reason, the last Hickman's design and my own have those small slanted chines. Strakes could be dangerous and I don't think that they would reduce blowouts. Blowouts may happen in turns with the TX18 and with tunnel hulls. In a straight line, the flow to the prop is steady, regular but in turns, you will always have turbulences and the only way to avoid blowouts is to take wide turns.
Did you try different height settings?
Jacques Mertens - Designer
http://boatbuildercentral.com

Vundu
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Re: TX18 Foam core stringers, ribs and sole. Strakes.

Post by Vundu »

Hi Jacques,
Thanks very much for the indepth reply. I'll go through my pics and post them, and I think I have a video or 2.

The build was eventually done out of commercial pine plywood, of extremely low quality as thats all we could get at the time. As I had never worked with wood, or glass before I know I overdid the build, making a heavier hull. I also added more glass to the hull as per advise as I was considering a 90hp at the time. She eventually was fitted with a 60hp 4 stroke merc, and runs well. We are at 1300m altitude so I do think we have some reduction on performance due to weight and altitude.

She is an absolutely fantastic fishing platform, stable and spacious. I have taken her on a lake in strong winds with a heavy chop, and she had a suprisingly good ride and dry. I was very happy with her, and everyone that fished in her was likewise impressed with her.

Since the build I have found suppliers of quality foam cores in South Africa, as well as BS1088 grade marine ply. To ship from the USA would be too costly as I cannot find anyone that will do a part load in a 20 ft container.

I would love to explore a complete build in Foam core - if it had a weight benefit and you have the time to look into it, but am concious of your reservations. I would take your advise on this and if there is no benefit would go with a blend of foam core and ply as you might specify. I am happy to adjust the weight distribution as you might advise too.

Vundu
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Re: TX18 Foam core stringers, ribs and sole. Strakes.

Post by Vundu »

Sorry missed the height settings question. I made a 3 inch jackplate and we ended up with the cavitation plate set just below (10mm) the bottom of the hull and a standard factory aluminium prop. Out here we have limitted access to props, hydraulic jackplates etc. She turns well at speed. For this new build I will install a Hydraulic jack plate.

jacquesmm
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Re: TX18 Foam core stringers, ribs and sole. Strakes.

Post by jacquesmm »

Thanks for the report and keep us up to date on the progress of the scaled boat.
Jacques Mertens - Designer
http://boatbuildercentral.com

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