4 piece transome

[jheron]

Well my boat is coming along, all the old rotted wood and glass are gone and the hull is ready for new wood and glass What a freaking job that was!! <br /> Well I dont think I will be able to get the transome in in one piece so I am going to put it in in 4 pieces (2 layers of 3/4"ply) I plan on cutting each piece on a 45 degree angle to make a skarf joint on oposite ends of the transome say about 2' in from each end. I figure that if done properly the skarf joint will not weaken the transome at all. What are some of your valued opinions on my plan? I dont see any other way to get it in there? <br />I plan to glue the first 2 pieces in with thickened epoxy then the next 2 pieces ontop of them and then screw the snot out of the joints. <br />regards Jon

 

[petrolhead]

Re: 4 piece transome

Trying to visualise your scarf joints, the usual ratio for a scarf joint in ply is 8:1 or more, not 1:1 (45 degrees) as you appear to be planning.<br />And whatever you do don't "screw the snot" out of it, a glue starved joint will be weak, epoxy resin is very strong stuff, often stronger than the wood itself, and is very good at gap filling whilst retaining that strength.<br />You only need to clamp, or screw, the laminations until it just starts to ooze out round the sides. Tighten your clamps/screws slowly and evenly, starting from the centre and working outwards.

 

[jheron]

Re: 4 piece transome

Thanks for the advice petrolhead! I am not sure I am following what you mean by 8:1 do you mean that 45 degrees is to much angle? What would be a good angle to set the saw at if this is in fact what you mean?<br />Hehe I here ya about starving the joint my plan is to pre-drill with a countersink all the holes on the outer board. I was thinking about using 10X1/1/4" stainless screws about every 4" along both sides of the joint plus another row another 4" out from them... does that sound sufficient?<br />I am not much of an artist but mabie this will help visualise picture the backslash as the joint and the periods as the screws <br /><br />___. . \ . .<br />____. . \ . .<br />_____. . \ . .<br />______. . \ . .<br />Thanks again<br />Jon

 

[petrolhead]

Re: 4 piece transome

Oh I see, it looks like you're planning to join the sheet diagonally across its width? I had assumed that you would make a scarf joint by planing the ends of the sheets and joining them, does that make sense? Damn this is hard to put into words that cannot be misinterpreted!<br />Anyone got a URL where we can see a photo or drawing of a scarf jointed sheet of ply?

 

[jheron]

Re: 4 piece transome

{ / \ }<br /><br />Ok see if this helps Picture the braces above as the outer edges of the transom and the slashes as the cut I will be making in each piece of the transome(one cut per piece). so the sheet closest to the stern will have its end cut off on the starboard side about 2' in from the outer edge so I can get it in and the next sheet will have the other (port) side cut off so as to give the max amount of overlay for the joints... Does this help at all? <br />On another track I thought about using a biscuit jointer to connect the sheets. What are your thoughs on that?<br />thanks again<br />Jon

 

[G DANE]

Re: 4 piece transome

Basicly, I dont like any idea of using cut plywood and joints in the transom core. If absolutely impossible, I think your idea of putting the joint as far out in the sides as possible is the best, and of coarse in port side on layer one, starboard on layer two, etc would strengthen too. Stress wil be much lower in sides than center.<br />I can assure you, as Petrohead mentions, bond between two layers of plywood with a layer of epoxy wettet mat between, will be the strongest you can get. I guess the 45 deg cut angle will be fine, just figure which way the stress is headed on the transom and turn the joint after that.

 

[G DANE]

Re: 4 piece transome

Be sure to clamp the pieces before you screw, or the screws will create a void between layers.

 

[jheron]

Re: 4 piece transome

Ya I here ya I dont like it either but its my only choice with out having to seperate the boat and believe me on this boat that would be a task! <br />What do you guys think about the biscuit jointer? I remember my buddy got one a couple of years back and we did the stress test on some 1/2" pine and the pine board broke but the joint stayed intact <br />Thanks again <br />Jon

 

[mellowyellow]

Re: 4 piece transome

have you looked into a "pourable" transom?<br />will never rot again

 

[petrolhead]

Re: 4 piece transome

I would do your scarf joints as shown HERE . Note that the bevel is cut through the sheet rather than across it as you are planning. What you are suggesting is really just an angled butt joint, a proper scarf, or two staggered scarfs in your case, will be much stronger.

 

[Mark42]

Re: 4 piece transome

A few suggestions:<br /><br />- Drill hole in ply that the screw is passing through so that it does not hang up or bite into it. Will have a better vise affect.<br /><br />- Make a lap joint cut on the ends of the ply. This over-lapping joint will be much stronger than a butt-end joint. It is easier to do in plywood than scarf because of the layered construction of ply. <br /><br />- Be sure to use marine grade ply because it must meet a spec that calls for a denser ply construction with no voids or knots.<br /><br />Mark

 

[petrolhead]

Re: 4 piece transome

Make a lap joint cut on the ends of the ply. This over-lapping joint will be much stronger than a butt-end joint. It is easier to do in plywood than scarf because of the layered construction of ply. <br />

Are you talking about a half-lap joint Mark? A proper scarf joint is stronger, and the layered construction of the ply makes it so easy, if the bevels are not perfect the layers show as wavy lines, if the bevels are correct the lines are straight and parallel.<br />Clamping the ply sheets together, one on top of the other, and planing them all at the same time ensures the bevels are all the same, and saves loads of time too.

 

[Mark42]

Re: 4 piece transome

Petrohead,<br /><br />Yes, I meant a half-lap joint. Agreed that a scarf is stronger, but my experience with planing plywood is that it is difficult because of the alternating grain layers tend to hang up in the planer. Maybe I was doing it wrong.<br /><br />Mark.

 

[petrolhead]

Re: 4 piece transome

As long as the plane is sharp it shouldn't be difficult, but there are other ways to cut the bevels than a plane, such as a router or circular saw, or a power plane. A quick Google search for "scarf joint plywood" will come up with several jigs for all three tools which make it virtually foolproof, but scarf joints in 3/4" ply should be easy enough to plane without a jig, as the joints will be supported from behind by solid ply they don't need to be absolutely perfect anyway.

 

[jheron]

Re: 4 piece transome

Thanks for all your input guys!!<br />mellowyellow "have you looked into a "pourable" transom?" Sounds interesting... <br />I have already bought the ply all I could get was exteriour fur ply, as a result of reading lots of posts on this site I believe it will be sufficiant I do plan on drilling the outer sheet so as to clamp the 2 together properly I dont have a planer but I do have access to a buiscit jointer but I am getting no imput on this idea mabie cause its a bad one?? <br />Keep the advice flowing guys and thanks again...<br />Jon

 

[petrolhead]

Re: 4 piece transome

The way I see it, a proper scarf joint is as strong if not stronger than the wood itself, a supported scarf joint such as you would be making in this case will be massively strong, at least as strong as a piece of 1 1/2" ply in fact.<br />Your original plan of an angled butt joint (you called it a scarf, but it's really just an angled butt) is only as strong as the supporting block, i.e. as strong as a single piece of 3/4" ply, the actual butt itself has very little strength.<br />A biscuit joint may be a little better, but it will still derive most of its strength from the solid ply behind it.<br />Any one of these may prove strong enough, but the scarf will be by far the strongest, I'd play it safe and use that. Don't have a planer? Get a cheap power plane, they can be had very cheaply now, I know because I have one, and you'll find loads more uses for it once you have it.

 

[jheron]

Re: 4 piece transome

Thanks guys I will let you know how I make out this weekend <br />Jon

 

[zzub]

Re: 4 piece transome

West system has a free pamphlet that shows how to pc transoms together very simple & easy.

 

[jheron]

Re: 4 piece transome

Well I made the scarf joints on my budys jointer, they came out real nice! I only maneged to get a 4&5/8" Scarf instead of the recomended 6" but because it is going to be supported on both sides I am not concerned I will tell ya that the scarf joints are far easyer to make than I had thought, once we had every thing set up it took mabie 45 minutes to complete the 4 scarfs Well now I am off to coat the ply and get ready to glass them in tomorrow. Thanks for all your advice!<br />Regards Jon

 

[petrolhead]

Re: 4 piece transome

Sounds good, can we see some photos of the job being done?