Wood questions

[bearwen]

Hello All,
Well I am looking at building a 18' tunnel hull speed boat the plans are from the 50's mechanix illustrated. http://www.svensons.com the boat is the aquaracer. I plan to mod it the original is set up for racing and well I intend to widen and lengthen the cockpit. The boat was clocked at 72mph with a 135 hp OB. Ok here are the questions I believe the boat is to be built out of exterior grade plywood or marine plywood as for marine is the Meranti BS 6566 anygood? Ok here is the big question why can you not use regular ie southern pine plywood besides the fact its glue is not waterproof if you seal it well and keep the boat stored in the dry say my garage or carport and just recoat the cockpit, deck and hull ext every year then it should be dry and waterproof is not an issue and as for the strength I thought maybe just space the frames a little closer (they are 30" max now) and just put the stringers a little closer all should be good? Here is the biggest question what is the best thing to use to seal the wood I have looked a CPES and it seems good and then maybe varnish? I donot want to put fiberglass on it I want the wood look can you use polyurethane from low@s and then clear coat with a UV stable clearcoat (keep poly from yellowing)? can I just paint the wood with a clear coat maybe automotive type after Cpes? Well I am trying to build this boat with my son and we are trying to stay safe and use a small budget i already own a 150 hp OB so extra weight of frames and stringers are not a concern and also we are looking to get upto 5 years or so out of the boat with regular maintenance and just general care with dry storage then I will build another one with my youngest son ( hes not really old enough to help on this one) All input positive and negative is great.

Thanks and sorry so long

[Ari]

in the 70's all plywood built speed boat at my place are painted to prevent it from rot, some of this boat survived and in used today.Tunnel hull character while taking a corner is different from deep V.make sure the hydraulic trim for your 150hp is fast enough to enable you to round the buoys sharply( at close to 90 degrees angle).

[bearwen]

Ari,
Thanks for the input but like I said I will not be racing this boat just doing some skiing with the kids and pleasure (speed) cruising.
I still dont know why I cant use just regular pine type plywood (besides the non waterproof glue)if I seal the crap out of it and paint it very well and keep up with maintenance and repaint etc annually ( I figure if I seal it well and paint it and repaint annually then the non waterproof glue shouldnt be any issue) also just put more frames in so there are smaller gaps and more stringers to compensate for less plys? Does anyone have any input I am only looking to get 5 years or so out of the boat and by the way I live in jacksonville florida and the boat will be garage or carport stored. How about luan plywood?

[BOATMIK]

72 or even 50mph puts big loads on a hull. If you can find an exterior ply with a similar quality (particularly in the internal veneers) to a marine it may be OK.

But the reality is that there is a lot of money and labour that goes into building a boat. Using good materials is purely a way of protecting the investment you are making.

If you are whipping up a simple open utility boat or a canoe or a utility dinghy over a couple of weeks and don't particularly care if it dies the death after 3 or 4 years then economise, economise, economise. Such a boat soaks up little in labour and materials cost.

But I think it is a poor choice for a boat that takes significant labour and will have to deal with significant loads (in terms of shock loadings from hitting waves and dealing with rougher water surfaces at higher speeds - anything much over 40 knots is a high speed in my book - in terms of loading up the structure).

Protect your investment. Use good quality materials

Best Regards
Michael Storer

[millrtim247]

just a thought from a newbie,
but the extra cost of more frames, stringers, sealer, resin, tape, fasteners might equal the diference in price between regular ply and the right ply...not to mention the the cost of re-sealing it each year...

Plus I noticed that you were not concerned about additional weight because you had a bigger outboard. True, you might not have a problem getting it on a plane. But a bigger out board also means a heavier outboard that weight added to additional wieght of extra framing might have an effect on boyancy or handling at low speeds.

Again I am pretty green at boatbuilding. These are just two issues that popped into my head when I read. They might not even be issues. Sticking with the called for materials would also save you the time of changing the desing plans to have more stringers/frames...

I think it's awsome though that you are doing this with your kids. I wish you the best...

[lewisboats]

Plywood now ain't what it used to be....go with marine grade...It MIGHT match the old exterior grades used when the plans were first issued. 1088 should be right for this application...just the price isn't the same.

Steve

[Ari]

I have more experience with tropical wood like Meranti than Pine.What Steve of Lewis boat mention is true.If you built it with pine and cold molding it, should be real good I believe. Marine ply with paint do last very long if taken care off..5 years of trouble free..is tunnel hull good for ski towing ? I know..deep V is..the tunnel hull that I'am used to are all racing machine..equip with 3.0 litres Mercury..and a drum of petrol a day..!

[BOATMIK]

If you built it with pine and cold molding it, should be real good

1/ depends on the design specs
2/ cold moulding means more layers of ply - so if using a minimum of 2 layers the thickness is going to be up round 3/8" - too thick and heavy for this type of boat.

MIK