New guy, potentially stupid question on the JA 18

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russellmn
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New guy, potentially stupid question on the JA 18

Post by russellmn » Thu Jun 29, 2017 10:28 pm

I love the looks of the JA 18 (classic runabout/speedboat) and I definitely like the jet ski power... what I'm wondering is if anyone has attempted these builds in aluminum rather than plywood? I have the skills to do it in either (though I am far better with metal than I am with wood and fiberglass) but I just keep thinking of how cool it would look in bare, polished aluminum...

So, am I way off base thinking that I could basically use the patterns for the hull plywood and just make it out of the aluminum instead to fit the forms and bulkheads???



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Re: New guy, potentially stupid question on the JA 18

Post by Fuzz » Fri Jun 30, 2017 1:10 am

Welcome to the group :D
As far as I know there are no stupid questions other than the one not asked.
JM is out of pocket for a few days but building out of aluminium is pretty straight forward. If plywood can make the bend aluminium will also. The big kicker to this is JM does not design for aluminium so you will be on your own for plating and framing.
Buy the plans, they are really fair priced, and go for it. Would love to see a build thread. :wink:

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Re: New guy, potentially stupid question on the JA 18

Post by Jeff » Fri Jun 30, 2017 7:48 am

russellmn, Welcome to the Builders Forum!! I fully agree to exactly what Fuzz said!! Further, we have sold a number of plans for the JA18 and a few have been built but none from aluminium or at least not that we have been made aware of!! A number of builders use Jacques plans to build from aluminium but as Fuzz said, he is a stitch & glue wooden boat designer and builder!! Jeff

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Re: New guy, potentially stupid question on the JA 18

Post by TomW1 » Fri Jun 30, 2017 11:22 pm

Several of Jacques plans have been built in aluminum. However you are on your own for selecting the gauge of the different sheets required. Don't be afraid of doing it just make sure that you use the correct gauge of aluminum.
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses.

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Re: New guy, potentially stupid question on the JA 18

Post by BB Sig » Sat Jul 01, 2017 5:58 pm

And make a build thread here with lots of pictures! :lol: :lol:

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Re: New guy, potentially stupid question on the JA 18

Post by bateau-webmaster » Wed Jul 05, 2017 11:51 am

Russell,

Biggest issue I see with doing this would be joining the remaining fiberglass Jetski Hull to the aluminium boat hull. Then again if you have the right fabrication equipment you might just be able to rebuild the jetski motor/jet drive into a lighter, and more efficient compartment made from aluminium. Jacques simply designed this around cutting the Jetski at the bottom, and dropping it into a correctly fit hole in the hull.
Cracker Larry wrote:Build on 8)
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Re: New guy, potentially stupid question on the JA 18

Post by bateau-webmaster » Wed Jul 05, 2017 11:53 am

Then again as I recall, the bottom of the jetdrive itself on many jetskis is aluminium, so you might be able to weld it directly into the hull.
Cracker Larry wrote:Build on 8)
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russellmn
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Re: New guy, potentially stupid question on the JA 18

Post by russellmn » Sun Jul 16, 2017 3:06 pm

If I were to do it, I would build a new intake altogether and not try to bond the plastic/frp to the hull. This fall I'm building an aluminum mini-jetboat like they play with in New Zealand, would probably do something very similar for the JA-18...

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Re: New guy, potentially stupid question on the JA 18

Post by Deathroll » Wed Jul 19, 2017 4:42 am

I have also asked the same question. and looked all over the forums for answers. really looking for someone to say "yeah its fine, go ahead!". but i couldnt. the problem i see is one of tolerances and gaps. from what i have gathered is that you can be a fair way off in the plywood and make the rest up with fillets and epoxy fillets, especially in the bow i have seen a lot of this.
I really wanted to build an aluminium plate boat, but the cost is too much (Australia) if you are wondering. So i decided to by the C19 plans. do them in plywood and fibreglass as shown on this site, and see how close all the panels get. I am a carpenter by trade and have only taught myself how to weld recently. i have built a pod for a 200HP outboard and its still together, but my MIG machine is not high quality( no pulse etc its great for steel, not so much aluminium), i designed, cut and shaped all the panels myself so there was nearly no gap. anything close to 3mm or 1/8" gap is too much for me on aluminium with that machine, sloppy welds and blowing out and having to do more passes. not one for grinding back and getting a good bond to the cold weld will undoubtedly make it weak and leak.
but if you have the time to shape and cut panels, add extra stringers probably 300mm spaced? and bulkheads at around every 600mm, 5mm bottom, 4mm sides id like to see it documented and i will have a go.
the only problem i can see is the chine. I haven't taken a look at your plans but i know on the boats i've been looking at you add a piece of timber with epoxy and fibreglass it in to make a spray rail/ chine. if you look at aluminium builds, it goes from the bottom panel, to a near horizontal panel(or at a reverse angle for a reverse chine??? i think its called) then the side panel. the bulkhead has a step in it if you understand what im going on about. if you were to just weld an angle along the aluminium there would be a void that salt water would sit in and eat away at the aluminium. and the strakes the same, they really like to avoid that.
I hope this helps but doesn't turn you off having a crack at the aluminium.
the only way i could do it was if it was CNC cut, but by the look of things jacques doesn't sell the cnc files etc. it would be great if he had an Australian supplier that he could trust with not onselling or giving away the files. I know a lot of the aluminium boat builders in Australia send your files to the aluminium supplier/cnc cutter to cut you 1 lot. or you pay an extra fee for a license to build as many as you like.

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