Transom rebuild question - Avon searider SR5.4

Dear All,

this is my first post, and I am novice in boat repairs (this is my first project). I am moving forward super slowly (as, super carefully), and I am learning a lot along the way. I have a question with regards to "how much should I cut" of the internal skin in my transom repair in a way I won't damage the structural integrity of the boat (thinking geometry-wise here).

The boat is an Avon Searider SR5.4 where the floor and transom where completely rotten and required replacement. I have read a couple of books on boat repairs and lots of manuals (plus a bunch of video tutorials - some of which I trust) however I still have some questions tailored to my project. This particular boat has a flooding hull design and I hope to restore it to its original state.

I decided to cut the internal skin (since I would replace the floor anyway) to remove the rotten plywood of my transom, as per other peoples advice and various similar projects I found online.

My Question is "If I cut completely the internal skin of the transom, will this cause problems of structural integrity in the corners / joints"? I have to cut in order to insert the new core material (either plywood or thermolite - haven't decided yet, probably thermolite). I have to note there is also a crack on the port side of the transom, that I have some ideas how to go about but please any comments / help most welcome. Please note, I am learning as I go.

Here is the present state of the transom. In my mind, there are two options for cutting. Leaving part of the internal skin of the transom, but then this requires to cut the plywood/thermolite to fit in inside the transom and glue it on he external skin.




The other option is to cut completely the internal skin of the transom, which will allow the plywood/thermolite core to be inserted in 1 piece.




And then, there is the crack on Port side to be considered as well, on how much I cut. Visibly, the crack only extends to the external side of the boat (where the pontoons attach with glue). I will sand the internal part to make sure there is nothing there (as well as external skin which is a mess - see for crack under the gelcoat).








Any advice/ideas/criticism please most welcome.

My main concern is the geometry of the fibreglass to be installed at the corners of the transom with the hull. Should I be better off leaving parts of the old internal skin (but there is a crack in the Port side! Shall I glass over it according to the standard methods of 12:1 bevel (or higher/as much as possible given the restriction in area). Or am I better off cutting completely the sides of the transom internally and replace with ply as in this picture (obviously glass everything on top afterwards)?



Thank you very much for your time.

 

Looks interesting, had to Google the boat to see what one looks like, this one is also a project:

 

Thank you @Tops - yes I've seen this video, very informative. Apologies I didn't put pictures of the boat in the normal state, this is the boat as it was purchased initially (and how approximately will go back - I'll change one jockey seat and there won't be that transom reinforcement any more):

 

Are you going to keep the flow-through water ballast system?
Does the rear seat act like a brace for the transom? The cracking seems to be consistent for a bigger motor without much bracing from transom to rest of hull.

 

Yes, the water ballast will be kept - I've removed the aft chamber intact and I plan to reuse it - the same for the bow one.

The boat is 1988, it was retubed in 2004 (the tubes are in excellent condition), but - even since then - it had that metal reinforcement. After removing it I found that the skin (rear and front) was cracked on the top of the transom, there was no ply - it was literally dust in 3/4 of the transom - especially on the port side where the crack is, and the outboard (90HP - max rating for this boat) was supported from the metal plate. There are two metal brackets that support the transom to the floor. This is the rear of the boat without the metal reinforcement - the transom had suffered long time ago some catastrophic breaking and they patched it - I can only assume. There is a similar crack on the starboard side on the front skin. The seat provides no support (nor it is designed to, on this boat) on the transom. The crack I assume is a result of the complete missing of the ply. Before the 90HP - at least in 2004, the boat had a 75HP yamaha - I don't know before that if somebody overpowered it.



The floor was all wet too, became rubbery soft when I took it in the water after 1 hour. When I opened up ...






the plywood in 7/8 of the floor was coming off like chips, complete delamination and no support.

This is how the support of the transom to the floor takes place, my boat has the same system (this photo is from another boat) but I assume it requires some form of plywood to exist:


On the plus side, the cruising was soooooooooo good, I just can't do anything else but fix it . I fell in love with this boat.

 

I went with option 2, as it would otherwise be impossible to clean the ply from the tight corners at the edges of the boat. I also found few other similar repairs that have done so on rib.net and elsewhere (and the boats still float so ...). This is the current state of the transom - needs more work for cleaning the wood remnants internally and sanding/preparing for the new core to be installed.



I also checked, I cannot see the crack internally from the transom, however the extent is a bit larger now that I further removed the pontoon - it was hidden under the pontoon previously:



I am not sure how to best address the issue of the crack. My strategy as I think of it now - please comment / correct me where you feel I am wrong - is to:

1. first install the new core bonding with epoxy (I plan to use 2 sheets of thermolite 19mm with fibreglass in between (probably double bias +/- 90 interchanged with +/-45 about 3mm thickness in total - as it was the original thickness. The repair will take place with epoxy resin, so I don't think I'll use CSM anywhere in that layer.
2. Then address the crack - I will sand the crack until I see healthy glass underneath. Then I plan to install fibreglass that wraps around the edges. There will be wrap around directions BA and BC. I plan also to extend the tabbing into the hull (internally) at least AB length. My thinking is that increased tabbing length (or else greater than 12:1 ratio) will provide more support to the transom from the floor therefore it will remove some of the stress from the crack point.




If you have any tutorials / books / chapters on how to best address cracks at the edges, or similar problems and how they were addressed, please share.

Thank you for your time.

 

Shoddy manufacturing is a bugbear of mine and this outfit has just hit the list.

Minor topic change are you intending to use that 4cyl Mariner outboard going ahead? They are poorly designed engines from the days of cheap fuel and zero emission requirements.

They are constructed of inferior alloy, engines poorly sealed from water, crankshafts poorly supported. Labyrinth seals wear out between cylinders and they won't charge. I could continue, but ditch it.

 

Hi @C. Dog , thank you for your response. The photo with the boat with the mercury is not my boat - I've put it for reference on how the transom is supported on the floor. My boat has a 90AETO yamaha 2008 with 40hours on the clock (looks new too - but yeah, I had my adventure in rebuilding the carbs there too as it was sitting for ... a decade?).

 

You should be a lot happier with the Yamaha than the old semi tower-of-death Merc. The Mikuni carburettors are a bit fiddly and prone to seized threads. Yamahas have very resilient water pump impellers, but a decade of sitting would call for a complete pump. Carbon in the impellers etches the stainless housing eventually.

At that age it should have powerhead gaskets and seals, 60 month service interval, so well due. It wouldn't hurt to reseal the bag of gears too if you're held up on the hull, often require oxy-acetylene heating to disassemble. There is no maintenance interval on gearboxes but they don't like water on the inside much.

 

I've done full service in the standard things (thermostat, rebuild carbus, impeller, gear oil and lubrication and of course spark plugs + lubrication). I agree with you on the gaskets and seals / retightening the screws, as per yamaha service manual - I'll send for that to professionals. That's a secondary goal once I sort out the hull, which is the major pain point at the moment. The boat when i took it out was flying, the outboard worked flawlessly (after carbu rebuild of course - 2 of them where stuck) - or at least it APPEARED to work flawlessly lol, I don't know what else to expect . Yamahas are very nice outboards, I agree, I had a small 30HP 2007 model with my previous rib (tiller steering). Never let me down - but I was taking apart carbus almost annually for cleaning (among other things).

 

There is probably enough expertise on here to get you through a powerhead reseal, but gearbox may be trickier. With the fibreglass cracking, grind it back a bit, sand surroundings clean as much as you can, use composite reinforcement appropriate for loadings, not my thing, but maybe find a local expert.

 

Hey mate, I’m restoring an old searider at the moment as well and came across your project. I grew up in Perth too but living in the US now. Did you find timber stringers when you cut everything open? Or any connection to the stringers between the transom and stringers? I ended up drilling and scraping out all the rotted transom and doing a seacast pourable transom, so I never got full access to the insides like you have. I’m worried my deck is shot too, might have to cut it all out like you’ve done.

Cheers
Sim

 

Hi @Simco - there are no stringers in the interior of my boat searider. There are buoyancy chambers glued under the floor, they are not in contact with the hull. I can give you the dimensions of the aft chamber - I'll know the bow one later down the project line, I have now cut half the floor and I am focusing on the transom. A lot of work, if your floor doesn't get water in, I wouldn't touch it.

You can see here in a previous state the boat:




This is where I am now, making pattern and preparing to cut the plywood that will replace the transom (I ended up with ply instead of thermolite for various reasons).


Check rib.net it has a lot of searider pictures and information and the FB Avon searider owners page.

I hope life is treating you nice in the US . Greetings from Perth
Foivos

 

You address the crack first, not last.

Before bonding the transom replacement pieces; see if the crack opens under torque. If it does; open the crack slightly and pour mixed epoxy resin into it liberally. Then remove the torque and the epoxy ought to run back up.

The seam is not tabbed properly. To tab it well, I’d recommend 4-5 layers of 1708. Each layer is about 2cm shorter, and the longest piece is first with a 5cm minimum on each side the sole and transom skin. For five pieces; the last piece is 10cm and the prior would be 15, and the prior 20 and for 4 layers, 25cm wide across the entire sole/skin.

Then your plywood can be hogged out a bit for the extra glass, and then the plywood also gets tabbed same way, like 3 layers. I’d not allow the deficit under the new transom plywood.

If you decide the epoxy is enough, then tabbing the transom to the sole might be sufficient, but the crack is pretty bad and needs to he addressed before you make it inaccessible.

 

The question is whether the crack extends all the way. Tabbing as I drew is required. If the crack is only on the edge; then fix it with epoxy and 1708 on the ply side before fitting the ply. Extend the tabbing only onto the sole and transom of it is not the entire distance.

My drawing shows the tabbing for the transom, but this would also be done in the plane perpendicular to the crack if the crack is limited to the edge.

Let me know if I am unclear.