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Newboy
10-21-2016, 11:31 AM
Hi All

I am in the process of rebuilding the transom on my 1930s mystery mahogany outboard runabout. The outer 2 piece mahogany planks were in good shape so I left them alone. The problem was the inner plywood transom piece was badly delaminated an I ended up cutting the knee to get the thru hull bolts out. The bolts were bedded with some kind of rubbery goop and just bounced when I tried to tap/pound them out. Anyway, that's all done and the new parts cut and ready to be installed.

1. Should the new inner plywood transom be bonded to the original mahogany? The one I removed was not, just held in place by 1 thru-bolt and lag screw on both the transom and keel.

2. Should the knee be bedded or bonded? the old one was bedded with the rubbery red goop mentioned above and at some point filleted with 5200. I am planning to drill the bolt holes slightly oversize and coat the bolts with a thin film of 5200.

I'll post a couple of pictures later

thanks

wizbang 13
10-21-2016, 11:53 AM
Plywood from the 1930's?
Yea we need photos. Boat size, engine size, use.
Oversize bolt holes are usually best filled with epoxy, THEN after hardening, re drilled. 5200 is a bad idea.

Jay Greer
10-21-2016, 11:58 AM
You might consider not using plywood again as it does have an annoying habit of failing and causing all manner is mischief for those who must later correct the problems it creates. But if you do choose to use plywood again, be sure to seal all the end grain and faces with either two coats of thin shellac or clear penetrating epoxy. Shellac will work just fine and is much cheaper than the epoxy. It can also be reversed with alcohol. Expoxy is highly resistant to any normal solvents that are not toxic to both the lungs and skin.

As for bedding the bolts, it should be obvious that the product that was used was not intended to need removal and so produces more frustration and the expense of extra time for removal. The way of bedding bolts that has always worked for the past several hundred years, or more, is to bed the bolt heads by wrapping a single strand of candle wicking or caulking thread that has been soaked in linseed oil under the bolt heads or washers. This produces a tight seal and allows for easy removal of the bolt should it ever again be necessary. For added insurance, a dollop of Dolfinite can be added as well. Some pictures would be appreciated in order for us to really see what you are dealing with.
Jay

Newboy
10-21-2016, 11:32 PM
Second attempt, apologies if my first reply posts too.

The boat is 14.5 feet, outpoard. No motor yet, but will probably stay in the 20/25hp range should it ever see the water again.
I was given a piece of 3/4" marine plywood by a local boat shop. It looks to be plastic on one face and plywood on the other, but the logo wouldn't sand off so I laminated a piece of 1/8" ply to that face for appearance sake. I painted everything with CEPs before laminating and will go over the edges before installation.

What about bedding the knee to the transom and keel stringer. Epoxy for strength?

here are some pictures:
Before image>
www.amazon.com/photos/all/gallery/VxnVkk4jRq6AgPNzx1FQlg?sf=1&ref=MS_US_W_P_P_A_CD_W_416_GSHB
After the tear out and cleanup>
www.amazon.com/photos/all/gallery/tHrlSGoZQT2yOF4eQtNMUw?sf=1&ref=MS_US_W_P_P_A_CD_W_416_GSHB&pageIndex=0
The test fitting>
www.amazon.com/photos/all/gallery/cWFNmY2CRDuWVVK_9VtRHg?sf=1&ref=MS_US_W_P_P_A_CD_W_416_GSHB&pageIndex=0

wizbang 13
10-21-2016, 11:59 PM
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Newboy
10-22-2016, 12:07 AM
Pictures that were supposed to be attached to my previous post. Maybe these will work?

https://cnt-01.content-na.drive.amazonaws.com/cdproxy/templink/9XpZhemkZ-Ubsc0dtY-yjFvCrDc53AdpMOWNvtddyt8pX92IB?viewBox=1098,824

https://cnt-01.content-na.drive.amazonaws.com/cdproxy/templink/OffNJqBTfBk9jb2_a-Z0K8DtV9yyIa6rEn2Vyky08VQpX92IB?viewBox=1098,824

https://content-na.drive.amazonaws.com/cdproxy/templink/VOneJGXT7M7eJ1Fvg6hpoqSD6ooVKb3F3Y0OajJR_gIpX92IB? viewBox=1098,824

wizbang 13
10-22-2016, 12:11 AM
https://cnt-01.content-na.drive.amazonaws.com/cdproxy/templink/9XpZhemkZ-Ubsc0dtY-yjFvCrDc53AdpMOWNvtddyt8pX92IB?viewBox=1098,824htt ps://cnt-01.content-na.drive.amazonaws.com/cdproxy/templink/OffNJqBTfBk9jb2_a-Z0K8DtV9yyIa6rEn2Vyky08VQpX92IB?viewBox=1098,824ht tps://content-na.drive.amazonaws.com/cdproxy/templink/VOneJGXT7M7eJ1Fvg6hpoqSD6ooVKb3F3Y0OajJR_gIpX92IB? viewBox=1098,824

wizbang 13
10-22-2016, 12:14 AM
I would omit the piece of ply , it does nothing. The cut outs for the deck knees....bad engineering.
Put 2 or 3 smaller knees on the bottom to transom. Be sure the gas tanks and battery have a place to live.
Also, the transom to deck knees are very important. Each of those ribbands could use at least a cleat.

wizbang 13
10-22-2016, 12:22 AM
Start em like this
https://farm8.staticflickr.com/7213/7091681615_8262c26340_z_d.jpg
keep building up,
https://farm8.staticflickr.com/7181/7136874445_7f3c5ff59e_z_d.jpg.
The knees are even more important with no aft deck.
A big nog of wood with a few bolts may not spread loads well enough.

Newboy
10-22-2016, 07:49 AM
I would omit the piece of ply , it


Also, the transom to deck knees are very important. Each of those ribbands could use at least a cleat.
I'm unclear on what you are referring to. Are ribbands the same as the horizontal battens and what would the cleat look like?

Peerie Maa
10-22-2016, 07:56 AM
I'm unclear on what you are referring to. Are ribbands the same as the horizontal battens and what would the cleat look like?

Don't worry about it. The ribbands are the ford and aft stringers (battens). They are well housed in the transom fashion pieces, so are adequately supported. After all there is no sign of failure after all of her years of service.

debenriver
10-22-2016, 10:57 AM
It would be good to have a quarter knee each side though, joining the transom to the gunwhale. It sort of looks like there were originally knees there. I would guess the ply is a later addition anyway.

Cheers -- George

wizbang 13
10-22-2016, 01:51 PM
A 1930's boat would have had a 5hp, maybe 10.
We do not know how much use she had.
She seems to have never had a clamp.Minimal tumblehome.
I would lam some strength in that was never there.
bruce

Newboy
10-22-2016, 10:21 PM
I have remade the quarter knees, they just weren't in the photo. The 'original quarter knees were attached with one screw through the gun rail and a few rusty finishing nails. I will be replacing and reinforcing all the supporting parts. The boat had a 1960's Johnson/Evinrude throttle/shift controller installed. Maybe it was about that time that the old plywood inner transom and maybe the knee was installed. The boat has oval cutouts in the outer transom for the 30s style external steering controls, but there were no cutouts in the plywood. More clues that it was modified. Thanks for the insites, maybe I'll get this thing figured out yet. Next step is to drill holes in the new knee get it ready to install. This is in conjunction with repairing the aft deck cross members, scraping and sanding more of the inside hull, getting the trailer sandblasted and painted, making a bunch of other supports, filling old fastener holes, coating the lot with CPES and so on...