Zodiac Futura - Transom done for?

[dhaglund]

So apparently this is what happens when you buy an older Zodiac Futura that came with a 15 hp Parsun tiller 4-stroke. The Parsun was quickly replaced by an 18 hp Tohatsu 2-stroke, just because I didn't like the Parsun. Unfortunately it is near impossible for find a decent short shaft engine so the 18 hp Tohatsu is a long shaft. So a transom extension was fabricated and this seemed to work pretty well. But then the teenage son (using the boat most of time) wanted more power and I wanted a quieter motor so the light Tohatsu was replaced by a heavy 25 hp 4-stroke. Still a long shaft.

Yesterday I removed the engine from the boat because the transom extension was bent. Not badly, but still very noticeable. Only to find that the transom now has a slight banana shape to it and vertical stress cracks around the four mounting holes. See the pictures. Apart from the obvious signs the transom seems solid.









What do you think, is this transom done for? Do I need a transom replacement?

[Peter_C]

What year is the boat? The cracks looks to be superficial as they should only be in the outer layer of ply. Plywood doesn't crack from layer to layer typically. Doesn't look like water damage from across the ocean, but is there? Did you use a sealer when bolting the motor on? I would recommend sealing up the exposed wood of the holes with Epoxy even if you have to slightly enlarge the holes, and redrill, then use something like 3M 4200 as a final seal.

Do you know for a fact the 2x4 is straight? Might want to use something made of metal to determine straightness, or at least rip an edge off the wood and then use it (Tracksaw or tablesaw would do a fine job). Kinda hard to figure out how such a thick piece of wood could warp without water intrusion and even then...

One factor that is hard for us to determine is what you extension looks like?? Also you need to support the transom when the boat is parked. I trimmed my motor down and put blocks and shims under it until it was well supported. Always towed with a transom saver in place too.

Without seeing it in person it makes it hard to judge, but personally I probably wouldn't touch it, and perform the repairs with Epoxy and sealer when reinstalling the motor. Then take it out and enjoy it.

I reglued the floor and transom on a Zodiac which was a BIG job. Not something I would do unless absolutely necessary.

[Steve509926]

Originally Posted by Peter_C

Do you know for a fact the 2x4 is straight? Might want to use something made of metal to determine straightness, or at least rip an edge off the wood and then use it (Tracksaw or tablesaw would do a fine job). Kinda hard to figure out how such a thick piece of wood could warp without water intrusion and even then....

I've read and re read this post and can't see where 2x4 is mentioned? Is the extension made from 2x4?

[paintman]

Think he's referring to the piece of brown wood being used as a straightedge to show the bend in the black transom?

Although the OP makes no reference to its size.

[Steve509926]

[dhaglund]

Originally Posted by paintman

Think he's referring to the piece of brown wood being used as a straightedge to show the bend in the black transom?

Correct.

I used that piece of wood just because I could cut it to length and take a good picture. I checked the warping first with some square metal tubing but it didn't work for a picture. Also the warping is clearly visible when looking at it from the side. Also, I don't trailer this SIB, we just walk it down to the lake a few hundred meters.

[dhaglund]

The boat is from 2002.

I agree that the cracks are superficial. I'm more concerned with why they have appeared in the first place. I can't see any signs of water damage. The boat is always stored inside when not in use and the transom is supported. The engine is tilted all the way up.

The transom extension can be seen in this thread.
https://www.rib.net/forum/f50/transo...ble-87202.html

So far I have only glued half a meter of the floor and that was surprisingly easy. A new transom would of course be tons more work. Especially since the transom needs to be fabricated. One possibly big benefit of redoing the transom is that I could make a long shaft transom.

Sealer has not been used properly before, neither by me while experimenting with different motors. I plan to seal everything with Sikaflex 571 when I finally decide on which motor to use. Since the boat is only in the water for an hour here and there this shouldn't be all that bad.

As far as I can tell I have three options.

1. Replace the transom with a new one designed to take a long shaft motor. - This is a lot of work and cost but would give me a better transom with new glue instead of 20 year old glue.

2. Make a better transom extension and build some sort of transom brace to relieve stress. This is less work than option 1.

3. Keep searching for that light 30 hp short shaft tiller engine in good shape that is near impossible to find. And still add some form of brace to make the transom straight again.

[Peter_C]

The bend in the transom is nothing I would be concerned with *shrugs* Odd that it is bent, but will it actually effect anything? I would guess not.

The cracks in the transom should be filled so they don't get bigger. Epoxy would work, or at the least some kind of sealant like 5200 just to keep water out.

Although you say the transom is supported my concern with the motor weight not being supported by more than the transom is the motor is continually trying to overturn the transom. Putting the leg down and supporting it from the ground up with blocking would alleviate any pull on the transom. I used a concrete brick of sorts, and a 2x6 block of wood to put a large portion of the motors weight onto the leg. Glue failure is a big issue with Zodiac transoms and floors. The rest of the boat is thermo welded and a non issue.

Now the transom extension seems to the problem you need to address as you say it bent. Yes a short shaft would solve your problem, but if you are going to make a new extension something heavier duty sounds in order. One option would be to drill down thru the extension into the transom and glue some steel all-thread in. Otherwise some heavier duty aluminum or the like to beef it up. How is the extension bent? Curious what is max HP for the boat? I know the larger 4.2m ones are 50HP.

[dhaglund]

The Zodiac Futura mark 2c is rated for 40 hp and 96 kg. So even with the heavy 25 hp engine at 83 kg I'm within that limit.

[69cmw]

Originally Posted by dhaglund

The Zodiac Futura mark 2c is rated for 40 hp and 96 kg. So even with the heavy 25 hp engine at 83 kg I'm within that limit.

Is that the rating before or after you dicked about with the transom? [emoji848]

[Jon Tallis]

Sorry Dhaglund, but IMHO those that are saying that a spot of epoxy filler will sort this out are mistaken. Photo 31 seems to show a crack that has propagated from one of your top mounting holes a way down the transom, and more significantly through several layers of ply laminate. The only way to stop that crack is to cut it out and replace it with sound material. If you just fill it and put your transom extension back on I can guarantee it will continue to crack. Your design of transom extension is concentrating the engine loads onto the centre of the transom leading to local stress-concentration and cracking.
You can of course bodge this up and hope for the best but if you want to sort it properly, I see the following ways forward.
* Establish the full depth and extent of the crack by excavating the transom with a router, also take a very close look at the corresponding point on the port side to check for a corresponding crack. Let in a section of marine ply sized really accurately for the section(s) you have cut out. Over laminate this with a marine ply pad 15-20mm thick, at least 50mm all round larger than a re-designed transom extension, with gradually bevelled edges to spread the engine loads more gradually into the existing transom without sharp corners or step-changes in thickness, which lead to stress concentrations and cracking. Bond all this in really well with marine epoxy, really heavily clamped until fully cured. Combine this with a much wider transom extension that spreads loads much better into the transom.
* Replace the transom including an integral, full width extension the correct height for your engine and of increased thickness.

[Steve509926]

Originally Posted by Jon Tallis

Sorry Dhaglund, but IMHO those that are saying that a spot of epoxy filler will sort this out are mistaken. Photo 31 seems to show a crack that has propagated from one of your top mounting holes a way down the transom, and more significantly through several layers of ply laminate. The only way to stop that crack is to cut it out and replace it with sound material. If you just fill it and put your transom extension back on I can guarantee it will continue to crack. Your design of transom extension is concentrating the engine loads onto the centre of the transom leading to local stress-concentration and cracking.
You can of course bodge this up and hope for the best but if you want to sort it properly, I see the following ways forward.
* Establish the full depth and extent of the crack by excavating the transom with a router, also take a very close look at the corresponding point on the port side to check for a corresponding crack. Let in a section of marine ply sized really accurately for the section(s) you have cut out. Over laminate this with a marine ply pad 15-20mm thick, at least 50mm all round larger than a re-designed transom extension, with gradually bevelled edges to spread the engine loads more gradually into the existing transom without sharp corners or step-changes in thickness, which lead to stress concentrations and cracking. Bond all this in really well with marine epoxy, really heavily clamped until fully cured. Combine this with a much wider transom extension that spreads loads much better into the transom.
* Replace the transom including an integral, full width extension the correct height for your engine and of increased thickness.

I agree with Jon. I think it would probably be prudent to replace the transom as I very much doubt a repair would hold up.
I think the weight of the OB and the extra leverage caused by the transom extension is exerting a greater force than the transom was designed for.

[dhaglund]

I agree with Jon and Steve.

Even a new transom can flex under load. Nothing wrong with that. But this one is permanently warped. To me that says that it is not structurally intact anymore. It is clearly weaker than it once was.

Having said that, I took the Zodiac out today with the light Tohatsu M18 mounted 30 mm above the transom which is the perfect height had it been a short shaft outboard. I only lost 1,5 knots or so top speed running that low! And transom flex was very minimal, even in chop. So engine weight and transom height make a big difference. No surprise there.

I could probably remedy this problem with some carefully drafted reinforcements or possibly repair by replacing a large part of the transom. But I would still be left with 20 year old glue holding the transom.

My conclusion is that this transom is near end of life and that I might as well replace the whole transom with a new one designed to take a long shaft, since it is far easier to cut a transom down if necessary than the other way around.

Should I find a good short shaft 30 hp engine, then this transom would probably survive a while yet.

[Peter_C]

Well I blew up the transom photo and that crack is far deeper than one layer of ply, but it was hard to see on a smaller screen. That crack is deep. See photo below.

If making and gluing a new transom to the boat, finishing to replace what floor glue hasn't been replaced could be done at the same time. Either way it is a ton of work.

[spartacus]

I reckon that transom is only going to go one way, it’s just a question of time. If the rest of the boat is mint and you’re DIY handy, then it can be replaced. Either that or cut your losses and shop around.

Only downside from repairing at this time of year is low ambient air temperatures and high humidity. You can certainly do the preparation though for a rebuild, unless you have access to a well ventilated heated garage.

As mentioned it should be good for 40hp which is a lump. I just wonder if it’s been trailered in a previously life? Peter C uses a transom saver from memory which seems to be the norm state-side. I used to build mine for the summer holiday, so although it had a Yamaha 25hp 2-stroke on it, it was never stressed with the engine in the raised position.

[dhaglund]

Peter C is absolutely correct, the largest crack is almost all the way through. I don't know if this boat has been trailered a lot before I got it or what motor was on it originally. But I'm pretty sure the transom was straight (or close enough) when I first had it. Things definitely took a turn for the worse when I put that heavy Tohatsu 25 EFI on the transom extension. That heavy but excellent Tohatsu is sold now.

Even though the best thing would be to replace the transom or at least replace part of the transom, both options require a lot of work. As you have pointed out. To begin with I will just reinforce the transom as it is with aluminium square tubing. That will have to do for now.

But the first thing to do is to straighten this banana-transom. So I righted the transom using threaded rod and some pieces of wood. I'll leave it like this for a few days to make it easier to attach the reinforcements.


I will put the square tubing directly onto the front of the transom as high up as possible. It will extend from tube to tube.

[Oldman2]

Assuming the transom is soundly attached to the tubes and down below & its just torque damaged in the mid upper section why dont you have 2 alloy or stainless plates made that cover near all the area of the transom and sikaflex and nut & bolt through in all the right places making a sandwich of the original transom with alloy box section bolting the 2 plates together at the top of the transom if any extra height is needed. You may get a couple of seasons from this or more.

[Peter_C]

dhaglund, do you have a router and are you comfortable using it? Cutting out the damaged section plus a lot more would allow you to overlap with ply and build in your height extension. Some round stock metal like All Thread glued inside holes would give the extension further strength. I'd agree a plate on the top bolts that goes far past the bolts width wise on the inside would help.