Pontoon Boat & Deck Boat Forum

Lakerunner might be able to help me with this as i think he posted on the other site about his repair. But anyone else who may have suggestions please let me know.

Here is a picture of the transom a few years ago. You can see that the wood is swelling and cracking the laminate cover. It has gotten a little worse so I would like to replace it before this season. You can also see how the bottom of the transom sits in the water. Since my boat stays in the water all season this problem contributes to the advanced aging of the transom.



I have some 3/4" MDO plywood available. MDO is made for exterior use so I think it has the appropriate glues to hold together in the moist environment.

http://video.bobvila.com/m/21315241/mdo-plywood.htm

I guess I would like to replace to similar thickness, but what is the maximum? i.e. what size are the motor designed to hang on?

The motor has a lifting loop so I plan on getting a motor lift to hold during the replacement process.

I'm not familiar with MDO but as far as the maximum thickness I would imagine the thickness that still allows the top of the outboard to slide onto it. My transom is all aluminum. I just went out to measure it. The top lip is 1 3/4" and where it mounts it is 1 5/8" thick.

Heatman,
thanks for the info, I imagine that thickness is standard so any motor can be used.

definition from Plywood Company

An EXTERIOR type plywood with a weather-resistant resin overlay bonded to the wood by heat and pressure. This process fuses the molecules of the overlay with the fibres of the wood to form a bond as strong as the wood itself. MDO has all the advantages of regular plywood as well as additional properties. The overlay, which has 28% resin content, resists water, weather, wear and degradation. It has texture that paint can grip with remarkable tenacity. Paint finishes on MDO are up to three times more durable than the same finish applied to ordinary plywood.Ideal for Painted Signs: In many instances, overlaid MDO plywood has proven a more durable sign material than metal. MDO plywood is resistant to the elements with no danger of rust or corrosion.

My transom if I remember was 1 1/2 marine plywood. I used 2 pieces of Treated 3/4. Using the old for a template I cut and drilled all holes ( I made them all slightly larger then original). After doing a pre-fit I fiberglassed between the two pieces. using bolts in their holes and c clamps on edges to hold it tight as glass set. I then knocked out bolts and cleaned the holes. I then coated the holes with some resin. I also added a thin coat of resin to outside of plywood. When I installed the new transom I added some additional strength by using flat aluminum on each side. My neighbor had given me a big chunk of alum plate 1/4" thick I cut to fit so motor brackets rested on the plate on outside. I used another piece on inside. I am kinda paranoid and tend to over build cause I am a lousy carpenter.

When I sold my boat to friend he took it back to Sundancer for refitting, new floor, carpet, console. wiring, and furniture. He ask about transom and said it was stronger than their own so left it alone. I also had a new problem develop when I went from 2 stroke 90 to 4 stroke 90. My transom began to sag. This worried me a lot and I fixed it buy buying a 8' piece of 2" angle aluminum. I removed the side rails and slid the angle through to other side. Checking the motor at full tilt I set angle so nothing interfered with it. I then jacked (floor jack with 2X4 cushion) till transom was at level where it started. I then bolted through transom edges to angle. When jack was removed everything stayed put. Sundancer also left that as it still held everything in place.

Do you have any names on the epoxy? I have found several things but none look like what I might expect.

What is the purpose of the epoxy? I assume seal out the water. wouldn't they also seal in the water if you get a damaged spot? I'm thinking about soaking the finished transom in some wood sealer.

Sorry wish, no idea the brand or name of epoxy. Main reason was to seal the 2 pieces together. The outside was to give more life and help waterproof I used glass matt on edges but the rest just the epoxy by itself

I would recommend Marine Grade plywood at least a double lamination of 3/4" thickness. I would glue the laminations with a layer of epoxy mixed with Colloidal Silicon (West Systems 406). I would then completely seal the exterior surfaces of the laminated transom with epoxy. As for the bolt holes, drill them oversized, tape wax paper on the bottom side and fill the holes with epoxy resin. After curing, re-drill the holes to the correct size. This will provide "waterproof holes".

After the epoxy has fully cured, (usually 3-4 days) sand the surfaces with #150 grit paper and either paint or apply a good marine UV protective spar varnish. The epoxy will seal the water away from the wood, but if left exposed to UV rays, it will be destroyed.

I use MAS epoxies, but others will work as well. I would recommend a slow cure hardener as they tend to be more flexible over time. Some of the Fast hardeners may become brittle and might crack.

Good Luck with your transom replacement!

Woodenpontoon, got any pics of the finished pontoon yet?
BTW, got my boat back with the new engine. Course it's just sitting in the driveway now, till Spring.

Parasympathetic wrote:Woodenpontoon, got any pics of the finished pontoon yet?
BTW, got my boat back with the new engine. Course it's just sitting in the driveway now, till Spring.

No pictures of my finished boat yet, mostly cuz it's still not finished!!!!!! I do expect to post some new ones within a few days. I am putiing the finishing efforts into the first fence section and 2 of the 3 gates.

Glad to hear that you got your motor replaced vs repaired. Much better deal!

Well, I won't know till spring if the new motor is the thing. I am glad for that vs rebuilt at the dealer.

Get those pics posted, I'm anxious to see a finished or close to finished product.

Wish
I would only use Marine grade plywood and since your boat is in the water I would fiberglass the wood before mounting it on the Aluminum.

Ya, id love to see more of that wooden beast!

WP,
do you know the difference between MDO and Marine plywood? I think the glues and the layering are the same but the difference is the outer coating.

I'm going to stop by the local lumberyard (not HD or lowes) and see what they know.

wish2fish wrote:WP,
do you know the difference between MDO and Marine plywood? I think the glues and the layering are the same but the difference is the outer coating.

I'm going to stop by the local lumberyard (not HD or lowes) and see what they know.

I don't know about the glues that are used or if the layering is exactly the same. Marine plywood has seven layers of veneer that are laminated together. All layers are wood and the finished board is supposed to be free of voids. Treated Marine plywood can also be found, which greatly increases the life of exposed wood.

MDO (Medium Density Overlay) consists of internal layers of veneer and as you said the outsides are fiberboard overlays. The fiberboard has no wood grain and is very smooth. MDO is often used to create forms for concrete work. Typically, used 1 time and then discarded. There is also a product called HDO (High Density Overlay) which is similar to MDO but has a stronger coating. I do not know if either of these products come treated for exterior exposure, nor do I know if the layering is "voidless".

I would not recommend anything but Marine Plywood for boat applications.

Hope this helps!

w2f, if it was me, i'd look for an old thick piece of aluminum and buy a welder friend a big fat steak to install it.

lr, "My transom began to sag." -- sorry to hear that, next time maybe try this.