question about aluminum for boat transom

[rfuerst911sc]

I have a early 70's Boston Whaler that I purchased as a fixer upper. At some point in the past someone had done a partial transom replacement it looks like the top half was replaced. The nearest I can tell it was done well and is solid and dry. I am at a point where I'm ready to hang the outboard motor but just to be extra safe I'd like to install some aluminum on both sides of the transom so the motor is clamping to the aluminum rather than the fiberglass. Boat will be trailered and only used in fresh water. In this scenario does it matter what alloy I use ? Should I use a 5000 or 6000 series ? I'm thinking of using .100 thick and it will have adhesive caulk and some screws drilled through the transom to hold it in place, plus the motor clamps and thru bolts. I'm probably over thinking this but I have a lot of time in this hull and want to be extra careful with the motor install.

[Roosterrusek]

Dude, got to tinboats.com is available - visit www.tinworm.com. Check out the Modifications forum....tons of awesome ideas and guys to answer questions.

[Roosterrusek]

Oops.... www.tinboats.net

[rfuerst911sc]

My boat is fiberglass.

[URY914]

If only in fresh water it shouldn't really matter the grade of aluminum. The best bet would be stainless steel. A steel fab shop that handles commercial kitchen work would be able to help you.

[Radioactive]

1/8" Stainless Steel.... polish it, it will look pretty.

[drcoastline]

If it were me I would be looking into the transom damage. The only reason people add metal sheets as you describe is because the transom is failing. This is usually due to core rot. The problem is by adding the sheet you redistribute the weight. As the boat flexes this creates an issue as the metal is more rigid than the fiberglass so now you have this piece of metal with a motor attached to it flexing the fiberglass transom that is already weakened by rot. Adding a second sheet on the inside is only going to compound the problem. If it hasn't already started the flexing is going to tear and deliminate the fiberglass. One day this will completely fail.

Why don't you take the time and cut the exterior laminate free from the core. Replace the damaged core and rebed the laminate? On a little Whaler this is a weekend project. It will look better and you won't have to worry about your outboard motor falling off the back one day.

[GO DAWG GO]

I agree with the others on the Cres stainless steel. Try to get some 320-321 Cres steel from a supplier. You can get it polished. This will not incur any corrosion, even in salt water.

Otherwise

The aluminum: Most yards will have aircraft quality 6061-T6. This is tempered and will work fine. If you can ask for some 6061-T6 CLAD. This will be coated with pure aluminum and will have a mirror finish. (We used it on American Airlines fuselage and wing skins..and it still looks great.

If you want to paint it, you will need to abrade the surfaces with 320 grit paper and then alodine it ( Alodine 1200) finish with a primer coat of Zinc Chromate or Epoxy based primer. Then you can paint any color...

Sounds like a pain in the you know what, but its the right way to finish aluminum.

thanks

Bob

[MT930]

Originally Posted by go dawg go

i agree with the others on the cres stainless steel. Try to get some 320-321 cres steel from a supplier. You can get it polished. This will not incur any corrosion, even in salt water.

Otherwise

the aluminum: Most yards will have aircraft quality 6061-t6. This is tempered and will work fine. If you can ask for some 6061-t6 clad. This will be coated with pure aluminum and will have a mirror finish. (we used it on american airlines fuselage and wing skins..and it still looks great.

If you want to paint it, you will need to abrade the surfaces with 320 grit paper and then alodine it ( alodine 1200) finish with a primer coat of zinc chromate or epoxy based primer. Then you can paint any color...

Sounds like a pain in the you know what, but its the right way to finish aluminum.

Thanks

bob

+1

[rfuerst911sc]

Went to the local metal shop this morning and picked up some .125 3000 series aluminum, I brought templates and they sheared it to size. Fit perfect I just installed the outer piece this afternoon. There is no rot in the transom it had previously been repaired. I'm just doing this as extra insurance and I think it makes more sense to clamp to aluminum than fiberglass. The transom is sound. I bent the aluminum to match the curvature of the Whaler transom and put a solid coat of Polyseamseal adhesive caulk and clamped it real good. I'll let it dry for a week and remove the clamps and then do the same on the inside piece. I'm hoping I don't have to add any screws/bolts other than the two that mount the engine. Hope to have the engine mounted by the end of the month. Thanks for the advice.

[URY914]

Post pictures or you will not receive any more free advice.

[rfuerst911sc]

Originally Posted by URY914

Post pictures or you will not receive any more free advice.

I'm at work right now but I'll try to get a pic or two of the " attack of the killer C- clamps !

[rfuerst911sc]

Arrived home and took two pics, not much to see but I guess it validates I'm doing the work. I haven't installed the inside piece yet that will be next week it is a little more square that the outside piece.

[URY914]

Verified.

Carry on.

[rfuerst911sc]

If Paul's happy I'm happy .

[URY914]

Let's see a pic of your nail gun now.

[rfuerst911sc]

Originally Posted by URY914

Let's see a pic of your nail gun now.

Haven't bought one yet but still looking. Lowes has a Dewalt roofing nailer for 159.00 that looks tempting.

[jschmidt63]

It looks like you have come up with some trategies for reinforcing transom and moving forward, best of luck. I own a 70 Katama Boston Whaler and have found some good resources through the years. One thing I have learned about is the internal wood reinforcment areas in older whalers through some great web sources. May not hurt to post your results for feedback on continuouswave.com.

BTW, it would be great if you could post the length, model, specific year, and make/hp/year of outboard, just love older whalers, they are like my older 911...

Again best of luck!

John

[rfuerst911sc]

Originally Posted by jschmidt63

It looks like you have come up with some trategies for reinforcing transom and moving forward, best of luck. I own a 70 Katama Boston Whaler and have found some good resources through the years. One thing I have learned about is the internal wood reinforcment areas in older whalers through some great web sources. May not hurt to post your results for feedback on continuouswave.com.

BTW, it would be great if you could post the length, model, specific year, and make/hp/year of outboard, just love older whalers, they are like my older 911...

Again best of luck!

John

John thanks for the interest in my Whaler. It is a 1973-1974 vintage I don't know for sure because when the transom was rebuilt the owner did not replace the hull serial number but it has the " smirk ". It is a 13 ' 6" and came with a stick steer system. I have purchased a Specialty Marine sport mahogany interior that is not installed yet. Have purchased a OEM stainless steel steering wheel. The motor is a 1987 Johnson 30 hp without trim/tilt. At this point I don't know if it runs but it's not frozen and has good compression. I bought this rig as a fixer upper project for $600.00 and that included a fairly new galvanized trailer so she owes me nothing . I have completely sanded the interior/exterior and applied primer and several coats of urethane white paint. I'm now just getting around to installing the motor so I can purchase the steering cable setup. Hope to have her in the water this year.

[jschmidt63]

Thanks for the info. guessing a 13 sport, very common and long running smirked and smirkless model. A few more pix probably could help you figure out model. Sounds like you have done some nice things to get her running and I need to do similar to my interior. Thats what I love about whalers, built to last, a shape that goes back to its roots and it set the standards for many to follow.

Classic Whaler: Boston Whaler: Reference: Specifications