restoring old mahogany small boat

Discussion in 'Powerboats' started by yli nick, Jul 31, 2018.

  1. Yellowjacket
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    Yellowjacket Senior Member

    First of all your boat is very similar to older racing boats that were around in the early 60's. What you will find is that these boats are very weight sensitive. You want to make sure you don't "overbuild" it as you restore it.

    Okoume is not as strong as mahogany ply like Sapele or meranti, but it is considerably lighter, the strength to weight ratio is better, but it is also soft and is easily damaged if you run over something. If you redo the bottom with okoume you should plan on putting a thin layer of glass on the outside AND on the inside. If you use 6 oz cloth you will add a considerable amount of strength to the Okoume, and the end result would be stronger and more damage resistant than just mahogany plywood. You should look for 5 ply as noted above it is a lot stronger.

    8mm on the decks is overkill. You should be looking for 5 mm or even less. Your deck has plenty of framing, you could go down to 4 mm and coat it with a single layer of 4 oz deck cloth on the top. A thin 4 0z deck cloth will disappear when you wet it out and it will help prevent the wood from checking due to sun damage. As noted above you need to use a UV resistant epoxy and then coat it with varnish that you can replace every 3 years or so to restore the UV protection.

    Too much weight, and in particular in the nose and the boat will be a dog.

    Also be careful as you take it apart, you need to make sure the bottom stays straight. To that end, do one part of the boat at a time. You've taken the front deck off, replace that, then do the side decks and the rest of the topsides.

    The transom is likely the next task, I couldn't see what shape the wood is in, but they typically rot and will likely need to be replaced. Same thing here, one part at a time. Then you can roll it over and attend to the bottom, and if you need to then do the sides. Make sure the bottom remains flat and true. If you get any hook or rocker in it the boat will plow or will porpoise.. If as you are installing the bottom you find it is warped or has rocker or hook, stop and fix it. You may have to make a jig to mount the boat on while you work the bottom. Once you finish the deck, roll it over and inspect the bottom and check for flatness.

    You didn't show pictures of the bottom, but the inside of the bottom looks pretty good. If the bottom is relatively sound, a good sanding and then epoxy and glass is all you would need to do. If you do replace the bottom, use a good thickened epoxy in addition to screws to install it. That way you don't need as many screws and it'll be stronger that it was when it was new.

    And don't even think about polyester. You're putting a lot of effort and time into restoring the boat, only use epoxy. When you consider how much money and time you'll have invested in the rebuild, doing it half a$$ed is silly.
     
  2. fallguy
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    fallguy Senior Member

    The Carver cold molded mahogany boats had 10 or 11 plies depending on the version.

    I own one from 1960 with 10 plies and it is still a running boat. Needs a stem repair though.

    I would use epoxy and 2 layers of 3 ply 5mm or a minimum of 10mm and joint staggering and a bog to avoid voids.

    If you use ss staples and encapsulate them in epoxy; they will keep the shape and never rust.

    I don't think any glass is needed, but it might be wise if there are joins unless you scarf joins at 12:1
     
  3. fallguy
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    fallguy Senior Member

    When you flip the bottom; you will need to make a temp frame for it so the boat doesn't lose shape on removing the plywood.

    Think a male station mold sort of thing.
     
  4. Yellowjacket
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    Yellowjacket Senior Member

    These boats were built generally with 5 or 6 mm ply on the bottoms 10 mm is overkill. The problem with Okoume is that it's soft. You can easily scrape it over a rock and crack the finish and let water into the wood, and screws tend to pull out of it. In order to waterproof wood you need enough epoxy to have a decent thickness. That minimum thickness is equal to what it takes to wet out 4 oz cloth. So there is no reason not to use at least 4 oz of glass since you get additional strength and really no more weight than if you just put epoxy on it. Going to 6 oz cloth adds a bunch of strength and is only a bit heavier than 4 oz and gives the bottom some protection.
     
  5. yli nick
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    yli nick Junior Member

    thank you all for your very good advices. a lot of very good information which i must take it in consideration.. thank you all very much.
     
  6. yli nick
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    yli nick Junior Member

  7. yli nick
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    yli nick Junior Member

    the transom is ok it just need some cleaning and an epoxy coat...
     
  8. yli nick
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    yli nick Junior Member

    I manage to find only 5 mm okoume, but i chosed to remain only at epoxy.
    i will cober the exterior in 10 oz fiberglass, and the interior in 4 oz fiberglass....
     
  9. yli nick
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    yli nick Junior Member

    the question is ??? shall i put the fiberglass on the plywood before putting it on the boat or should i put the 4 oz fiberglass at the intwrior after, and that means to also cover the ribs ....
     
  10. yli nick
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    yli nick Junior Member

    i will also replace the ribs, the middle one is 4cm by 2 cm. white oak..the others are 2 by 2 cm. the distance between them is 9 cm almost 3 and a half inch...so i think that the bottom will be enough resistant....but only my opinion...wait for your advices...
     
  11. yli nick
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    yli nick Junior Member

  12. Yellowjacket
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    Yellowjacket Senior Member

    You don't need 10 oz on the exterior, 6 is fine 8 is overkill. To fill 10 oz you end up with a lot more weight and that's not good for this kind of boat. If you want to bright finish the wood, you can stain it after you remove it after fitting and countersinking the screws. If you use the right cloth 6 or 8 oz cloth will disappear. 10 oz won't, you'll always see glass weave. Choose a fabric with an epoxy-compatible coupling agent, because it permits epoxy to more easily replace the air around the filaments than incompatible fabric. Use a coated cloth that is designed to wet out clear and bright finish will be the best looking imho...

    Note that you may have to scarf and bond pieces together to get one piece long enough. Don't assume you can but joint piece the ply, that'll be a mess.

    As to the 4 oz on the inside, given the spacing on your ribs it's likely going to be a lot easier to put the glass onto the wood first and then apply the wood. First you need to cut and fit the ply so that it's trimmed to fit properly and drill pilot holes and install enough pan head screws to make sure the ply doesn't pucker and is properly seated all around. Best to work from one point, like the transom and the keel and work forward from there. Clamps are your friend, use lots of them make sure it's all properly fitted before you start drilling pilot holes for screws. Before you remove the plywood, check the bottom for straightness. If there is any hook or bow in the bottom, jig the hull so that it's straight. Remove the wood and put small countersinks where the screws were on the outside and cut the glass to size. Then you can mix up mix up a batch of epoxy and wet out the glass on the wood, don't do a really wet layup, just use enough epoxy to wet out the cloth and don't make it too sloppy.. Next mix up enough epoxy to paint a coat of un-thickened epoxy on the ribs to get good adhesion. Last mix up a batch of thickened epoxy, and put a bead on the ribs. You don't need much thickened epoxy on each rib, just a bead that is about 1/4 of an inch wide at the most. Last flip the wood over and install it using the screws that you used to install the wood in the first place. You can use additional staples to make sure the wood is fitted perfectly. If done right, the glass and epoxy on the ply will be starting to gel around the time you finish all the other gooping, and it won't move around or pucker when you flip it over and put it on. It's important to have a second set of hand to help put on the ply. You want to put the ply on in the correct place on the first try and not slide it around or the glass on the inside can pucker and make a mess of things. That's why this is best done as a two man job. If the ply and epoxy is too hard when installing it can pull as you twist the wood into place. If it's not set up enough it can get pushed around and pucker when installing it. I don't use fast epoxy when doing this kind of job for sure. You have a lot of ribbing, so it may take a while to get the bead work done, so you'll have to work fast. If you want you can use slow epoxy, but you may have to wait a while for it to start to gel before you install it. Use an epoxy that is no blush, and after it sets up you can flip the boat over and paint a layer to fill the weave in the inside. If you do that within 18 hours you don't need to sand or clean blush off and one side will be done.... Rinse and repeat for the other side... After all is done you can put on the exterior epoxy and glass.
     
  13. yli nick
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    yli nick Junior Member

    thank you very much for your advices, i will keep you informed with my progress ..for the moment i will try to change the ribs.
     
  14. yli nick
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    yli nick Junior Member

    i managed to do the mahogany for the front deck... i made it 6 mm thik. should i put some 5 mm plywood underneath??? 20180814_221000.jpg
     

  15. Yellowjacket
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    Yellowjacket Senior Member

    Your deck already has a huge amount of ribbing and was designed to support the stripped mahogany that was on it without any underlayment. 4mm Okoume ply, by itself would be plenty on that deck and you could easily walk on it. You need to appreciate that these boats are extremely weight sensitive. With all the framing up there, you only need thin skin of decking. Many hydros and racing runabouts of that era used aircraft fabric for the front decking. Even 6 mm of mahogany is really too much weight and is unnecessary. Since the original decking was mahogany stripping you can use the old deck pieces for patterns and simply replace them with the new decking. Then to get it all smooth you can go at it with a heavy duty sander and don't be afraid to grind off a mm or even two mm to make it look nice and fair. Remember as you do your final sanding to only sand with the grain or you'll end up with sanding marks below the varnish. The biggest problem you will have is that the original decking wasn't equal width strips, in plan view these were wedge shaped pieces of thin mahogany. If you have equal width strips then you have the dilemma of unsupported edges of the stripping and that is a problem. If you are trying to be true to the original design, you would need to cut thin pieces the same shape as the originals. If you want to use equal width strips then your 6mm will probably work ok since it is way thicker than would normally be required, but that's not the way the support structure was designed. If you aren't going to be true to the original design, then it would be a lot easier to get some mahogany ply, cut it into two pieces, piece it in the middle and glue it down and be done with it.
     
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