Oday 25 Transom overhaul and repower

[btm0905]

Greetings
This topic is well versed on this forum in various threads, but I figure why not start a new one regarding my personal endevours.

So this all started with the idea of repowering my 1978 o'day 25 with a new 9.9 4 stroke Honda long shaft. I'm almost certain the original mount is stock, and most likely inadequate. (fighting the old 8hp Honda up and down gets old). The planned replacement mount is a new Garelick. Researching leads me to discover this will require a new spacing block. No big deal. Further reading reveals that a frequent problem that arises here is water intrusion and rotten core. So, off comes the old mount...and of course...my boat has water intrusion and rotten plywood...YAY!

So now I'm looking at rebuilding the transom and lower gudgeon which is also rotten due to leaking from the topside drain.

I've attached pictures, and will post progress as it happens...looks like I will be tearing out and replacing the starboard plywood and lower gudgeon plywood. Adding new blocking for a new motor mount, and resetting the lower gudgeon hardware. Does the best backing need to be 1/2" marine plywood? Or is there an easier and stronger material?

 

[svchickadee]

I replaced a rotten transom on my Oday 25 a few years ago. I had a new 'wedge' built out of 3/16 aluminum and installed that wedge and a new motor mount with a 9.9 Yamaha high thrust outboard. Last year I took the boat down the icw from Maryland to Florida and then over to the Bahamas all the way down to Long Island. There were no problems with the outboard. If you are interested in what I did send me a private message and we can talk.

 

[Brian S]

Since you are re-doing a motor mount, and you want easier function, I recommend you consider a Garhauer. They are available retail at http://www.catalinadirect.com/index.cfm/product/691/outboard-motor-mount-three-spring.cfm You can choose the number of springs to match the weight of the motor. The manager of Sage marine uses them on their new Sage boats, and explained to me many reasons he likes them over the typical Garelick.

 

[sdstef]

Looks pretty rotten. I had an Oday 25,1977 vintage. I caught my lower gudgeon leaking, and it was also cracked on a weld.. One good thing is that there is plenty of room to work down under the cockpit on that model.

 

[btm0905]

Can anyone give me a rough idea on how much epoxy this kind of repair would require? Also I'm now planning on using 1/2" treated plywood, and running a 45 degree brace to the fiberglass runner along the bottom of the boat. This would provide some extra strength behind the motor mount. (I figure this is OK given the age of the boat, and the fact that the transom will not be getting wet again). Also any tips on getting the plywood to bend properly while the epoxy sets. On another thread, the fix required drilling a dozen or so holes through the transom to suck the wood in tight while the epoxy sets. I would like to avoid this approach if at all possible.

 

[Brian S]

Bending plywood.... Well, there are kinds of plywood that are designed to bend. Like, the plies run in the same orientation. However, I think what I'd recommend for epoxying reinforcing ply in place would be to use multiple sheets of thinner plywood and laminate them to each other in place. West Systems recommends using microfiber filler for lamination. You want to make sure gaps are filled as well, maybe some colloidal silica mixed in with the microfibers would be good. Since epoxy is designed to bond to the cellulose of the wood, I've often used wood flour as a thickener (it's basically sanding dust.) My friend's whole kayak is glued together with wood flour thickened epoxy, so it's a fine bond. I don't know that treated plywood is going to do anything much for you, if we are thinking of pressure treated wood like for outdoor applications. Better to use BS6566 plywood, which is supposed to have no voids in plies, and to have thinner and greater number of plies per a given thickness than what you find at the typical home building supply place (big orange or blue box.) I have used 1/2" fir plywood which is "marine plywood" which essentially means it is glued with boil proof glue, that darker purple stuff. I don't care for it, because even if you soak it in epoxy, the fir face will still crack and check. The difference between BS1088 and BS6566 ply is 88 is A/B, and 66 is B/C, less expensive and more suitable for your hidden away work. Okoume is a common tropical hardwood, but it is not particularly rot resistant. Meranti has a rep for being more brittle, so I don't know that I would use it when I know I'm flexing it. Fully encapsulated in epoxy, in a dry environment, the okoume is probably nothing to worry about.

 

[Ron20324]

Bending... I had some 5mm and .25 plywood going to waste, so I used it to make rims for wagon wheels. I made a jig to bend them to 40"i.d., 42" o.d.. I found it worked well to put the 4" wood strip in the tub to steam while I showered (sorry, no pics for this post), then gave both inside and outside surfaces a quick coating with the hotest water to soften the surface plies. I put them on the jig to dry in the bent configuration. Then later glued up the laminates. If you can make a jig close to your desired shape, you could do the same. I used the good carpenters glue, but you want something different.

 

[Ward H]

Knowing the shallow curve you need to mate the plywood to, I suggest the layering of thinner layers of plywood, maybe 1/4" thick, coated with epoxy. You can bolt thru the transom to pull them tight. Wax or grease the bolts so the epoxy doesn't stick to them for easy removal when done. Fill those holes when done.
Round off the corners and edges of the plywood facing the transom so there isn't a sharp edge being pulled against the transom. This will help to reduce stress points I am told.
I would think a couple of holes to pull the plywood tight to the transom would be enough.

 

[btm0905]

UPDATE:
I spent the day ripping out the old wood and inboard fiberglass, and grinding away the old glue.
A few tools are must have for this. 1: Box fan, Placed over the access door to exhaust dusty air, nice to have when you need to sit up and take a break. 2: Shop vac, I'd say I ended up with over a gallon of white dust...cleaning as you go is a must. 3: PPE: Goggles, respirator, ear plugs, tyvek suit, gloves...This. is. a. dirty. job. 4: Grinder with a low grit flap disc, rotary Dremel with reinforced wheel, oscillating Dremel. A Sharp Chisel (chipping glue off is much more desirable than grinding) hammer, and pry bars.

 

[btm0905]

Update part 2:
So after an extensive cleaning (vacuum, rinse, repeat...) I was able to make a transom template with cardboard, and transferred the shape to a piece of plywood (getting the transom curve is much easier on the outside!) I ended up going with 1/2" BC Exterior plywood from Lowes for a few reasons.
1. Cost: I bought a 4x8 piece with a crack in the corner for $6. Apparently no one in Wilmington stocks 1/2" marine grade, and most quoted over $100 with at least a week lead time.
2. What i was ripping out looked more like T-1 11 than marine grade plywood, and it held up this long. Also, the new plywood will not be getting wet. Any penetrations will be drilled out, epoxied, and sealed with butyl tape. I avoided pressure treated because I was worried about encapsulating a piece of wood with such high moisture content.

The plywood is shaped, and clamped together overnight. I tapered the edges to encourage the fiberglass bond.

Now here's what I'm left with
1: Come up with a way to tie the cockpit drain back to the transom. At some point the two became completely seperated.
2: Come up with a way to fit the plywood around the drain in order to keep the wood continuous. To cut the drain, or not?!?!

 

[svchickadee]

On my 1976 Oday 25 the cockpit drain setup is two 1 1/2 inch mushroom head thru hull fittings connected by a length of 1 1/2 inch marine sanitary hose. The mushroom barbs point at each other under the cockpit. This setup would allow you to remove the glassed in drain making the installation of the new transom easier and stronger.

 

[Ward H]

Great pics detailing your work. I think they dumpster dived for that T1-11. Looks like my old house.
Very nice work. Now I know what I will need to do one of these days.

 

[svchickadee]

I will be interested in knowing how you get the new laminated plywood transom to conform to the curves of the boat transom. The new transom does not look like it has much flex to it. When I rebuilt my transom I rebuilt it from the inside of the boat (under the cockpit) laminating three 1/4 inch plywood sheets one at a time. The transom shape was maintained and I got a good, solid fit with no voids.

 

[btm0905]

UPDATE
The first layer of plywood is in! Started by fitting the first sheet in place and temporarily wedged it to stay with a few 2x4s. Back outside i drilled all the holes i would need through the plywood using the existing as a guide, and a few extra (2 in the paint stripes, and 1 below the motor mount to make repair easier) that i would end up using to thru bolt and tighten down the new plywood once glued. Then templated these holes to the second layer. I used a skil-saw to make 1/8" grooves on the back of the plywood to help mold the curve in the transom. A previous poster recommended making these in a 'ray' pattern, which i know helped!
Now for the install, 2 primer coats of epoxy on the back of the plywood. Next a quick Acetone washdown, a coat of Epoxy, and woven glass on the inside of the transom. Next used almost a whole container of West System 403 and smeared the entire face of the transom with 'mayonnaise'. Carefully fitting the plywood in place, I used a few bolts from the inside to line up the holes, then went outside and pushed the remaining bolts through. (greasing them up with Caranuba car wax apparently keeps the epoxy from bonding to the bolts) Tightened up all the bolts, and used a few 2x4s cut to length to wedge the plywood in place. A few things I would recommend 1) tape off any thing you might tough getting on and off the boat and through the door, the epoxy gets all over you no matter how hard you try not. Also get an old hat. I did not do this and now I look like Ben Stiller from "There's Something about Mary". Get an auto-ratcheting wrench. Over drill the holes in the plywood to help line up everything.

I cut out the cockpit drain, and plan on re-routing it down and out the port side of the transom using some thru-hulls...

 

[Ward H]

Looks like you are doing a great job!

 

[btm0905]

UPDATE
Started on the motor mount wedge. Had to make a wider one for the Garelick 71090 to fit into. (Made mine 9" wide by 10" tall, 4.25" deep) Used a melamine shelf from Home Depot and assembled, and used some LVL scraps as filler. Caulked the corners with some fast dry silicone and let it cure for about 12 hours. 4 coats of Carnabua wax seemed to be enough for a mild release.

Used 2 layers of woven glass, and epoxy and filled the mold. If I had to do it over again I would have made sure I had more filler, but ran out and only had enough to fill between the blocks. Once it was full to the top with epoxy I had trouble with air pockets, and and in the process of reworking the face that will sit against the boat. Also would have made the mold deeper than needed, and worked up a curve on both sides, rather than fight epoxy dripping out...Hindsight is always 20/20...or at least I would have cut the blocks smaller, in order to leave more room to grind out for the curve. I am now trying to build up the edges on the side after-the-fact....no bueno.

Good new is the mold came off relatively easy. The wax seemed to do the trick, although some of the melamine did end up sticking. I'm thinking this had more to do with the heat from curing than lack of wax, because it scraped off easy enough with a razor. More pics of this to come...

 

[sdstef]

Nice work!

 

[Ritdog]

All that grinding is fun, isn't it? - did that twice, new panels, etc., on two boats. I used 1/4" ply..... set the first, then 2 and 3 for a 3/4" panel. Came out bomber....same for the king plank. I did screws through the hull for a tight fit. You might want to do a tap test to see if there are any voids in there. Had a small one - drilled two small holes top and bottom, then put thickened epoxy in the bottom one with a hypo, pushing till it came out the top,

 

[svchickadee]

This is the custom mount I had built for my oday 25. The mount is extended lower toward the waterline to leverage the stringer on the inside of the hull running parallel to the keel line. Under power the mount pressures the stringer and not the transom.

 

[svchickadee]

2nd try for the image .