Replacing wood transom on Aluminum deep V boat

yam350yfm · #1 March 9th, 2009, 03:18 PM

I am moving the following to this forum as advised.

I just bought a mid-1980's 17' aluminum boat deep v fish and ski that has a 70HP outboard and the transom needs to be replaced. The wood transom is sandwiched between aluminum skins on the inside and outside of the transom. The center of the transom is pulling away from the splash well. I assume that was caused by water intrusion where the holes for the outboard are. It appears that there is an aluminum cap that is held in place with some small nail type fasteners that probably went into the wood. The outer aluminum skin has 20 or so fastener's of some type, some are screws, some are through bolts, and then there are some rivets. I have replaced transoms on fiberglass boats so I know how to form and epoxy the transom, I am just not sure how to remove the old transom on an aluminum boat. Here is what I think needs to be done:
1. Remove the outboard
2. Remove the outer transom board spacer that was added over the aluminum (oddly enough this is not rotted)
3. Remove the aluminum top cap (not quite sure how)
4. Remove all screws and bolts from the transom
5. See if the existing transom will pull out at this point

I am not sure how easy it would be to access this from the inside as there is an area that has the battery, oil tank, fuel tank, etc that would be in the way for access to the inner aluminum transom panel.

The transoms I replaced in the past were done with 3/4" marine plywood epoxied to seal them, including the holes. I planned to do the same with this one. I did price out Starboard composite but that was very costly. I guess another option would be to pour a transom with Seacast, just not sure how that works out on an aluminum boat.

Any tips or links to photos on how to disassemble, or pointers from those who have done it would be appreciated.

Starcraft Tony · #2 March 9th, 2009, 08:37 PM

Sounds about right, or at least thats how I did mine and it worked out just great(sorry no photos). Those "aluminum nail" things pop right out with a screw driver. I saved and reinstalled mine. The screws and bolts come out easy enough but there are a ton of them and this chore is best performed with two people as nearly all of mine spun (16' aluminum Starcraft). Save yourself the hassel and just cut any thru hull fittings and then that transom should pull out. Let us know how it goes, and good luck.

sschefer · #3 March 9th, 2009, 09:28 PM

On my 18' F/S I started from the splash well and worked back to the transom. There was no other way to get it out. I'm not sure what that inner skin is all about. I'm almost thinking it was added on unless it's actually part of the splash well.

3/4 Marine Grade ply or 3/4 Fir ACX ply will work fine. I do mine with a sheet of 3/4, a layer of carbon fiber wetted with resin and then a sheet of 5/8. I don't know if the carbon fiber is necessary, I've never broken one either way.
I'll bet when you get it out it will be in several pieces. I made mine into a single laminated piece but I don't know if that really makes any difference either since the original was in there for almost 20 years and it didn't break.

Bob_VT · #4 March 9th, 2009, 10:43 PM

Take a few pictures and post them. Forget seacast on the aluminum boat .....it would be way too much money for the result. 2 pieces of 3/4 plywood will last a long time if properly installed..... well only 20 years or so.

yam350yfm · #5 March 10th, 2009, 10:55 AM

Thanks for the tip on the through hull fittings...I can get replacements at Kendor. I was over there before I bought this project to make sure that I could get whatever I needed. In addition to Seacast I looked at Starboard but that was going to cost around $600 for the sheet of 1 1/2" thick material and when I called the manufacturer they did not know of any epoxy or adhesive that would bond two thinner sheets together they said it would require mechanical fasteners.

The local lumber yard can get me marine plywood for around $70 per 4x8 sheet of 3/4" thickness. I used exterior plywood (don't recall if it was ACX or CDX) when I did a transom on a fiberglass boat last year and that was around $20 per sheet. From what I understand the marine plywood has less voids and is sanded on both sides. It appears there are several types of marine plywood; fir, birch, and 1088 of which there area several varieties. Looks like some claim to be more rot resistant then others, not sure how true that is. The other supposed difference is that there are less knots and limited number of repairs (where the knots are cut out and replaced...those football shaped repairs).

Also thanks for the tip on the fiber sheet between layers, I may wrap the whole thing in fiberglass after applying a layer of epoxy to seal it all. The holes will all get sealed too. I am pretty certain the water intrusion was at the holes drilled for installation of the outboard.

I will photograph the process, including the initial damage so it can be loaded out to help others.

Onehorn Buttfish · #6 March 10th, 2009, 11:48 AM

I am closely watching this thread as I am also trying to replace the transom wood on a al boat. My problem is it is angles like a chris craft on the stern. Is it acceptable to make the replacement of 2 parts and use the aluminum motor mount plate to clamp them together. Maybe overlap the plywood in the middle like a lap joint. Attached a image of what I am up against.

Thanks for any tips.

Bob

yam350yfm · #7 March 11th, 2009, 10:47 AM

Onehorn....I have not seen an aluminum transom shaped like that before. You could try what you say, use a good epoxy such as West Systems at the seam along with coating the entire piece. You could maybe install the lower piece and then epoxy an upper piece to it. Not sure how much motor you run as to what I would be comfortable with in that situation.

I guess another option would be to use thinner plywood and laminate it yourself as you go. Something like 1/4" or 3/8" marine plywood should bend to that shape, then layer on the epoxy and install the next sheet and keep going until you have the necessary thickness. You would need to come up with a method to clamp it up while the epoxy sets.

Makes mine look much easier......

sschefer · #8 March 11th, 2009, 11:44 PM

Quote:

Originally Posted by Onehorn Buttfish

I am closely watching this thread as I am also trying to replace the transom wood on a al boat. My problem is it is angles like a chris craft on the stern. Is it acceptable to make the replacement of 2 parts and use the aluminum motor mount plate to clamp them together. Maybe overlap the plywood in the middle like a lap joint. Attached a image of what I am up against.

Thanks for any tips.

Bob

Bob, unless that picture is lying to me, that's an easy transom replacement. It only goes half way down. Pull the corner caps, take out the through bolts and slide it out. Build a new one and put it back. That's a two day transom re-build at the most. I can't see if those corner braces are riveted to the sides or not but if they are just drill out the rivets and replace them with 3/16" 18-8 stainless machine screws with nylon insert lock nuts.