Oil Canning Transom O'Day 35

[Dave Mauney]

I just noticed this evening, with the sun at the right angle, that I have oil canning in the transom associated with the back stay chain plate. The gel coat is not cracked but rumpled. Even though the tuning load that I used is well below the back stay component of the 30 degree righting moment, could this oil canning be from too tight a tuning load on the backstay? Thanks

Good Winds
DaveM

[Brion Toss]

Hello,
Remember, a proper tuning load is the same, or nearly so, as the load that the stay experiences under way. So if the wire is the right size, and the loading numbers are right, and the tune is right, then you are not imposing anything that the boat shouldn't be capable of handling. So if the backstay is deforming the transom, something is very wrong with that transom. What is the structure?
Fair leads,
Brion Toss

[Dave Mauney]

Brion

I appreciate the reply. What you said is what I thought. I used your advice before and went though all the calcs guided by The Apprentice and all made since. I used the loads for one wire size down, as the manual says they oversized the wire, and for the wire size in place and tuned right in between the two. Even with that I still get slack on the lea lowers. The transom is fiber glass. The loading on the chain plate on an O'Day 35 is pulling in on the chain plate top as well as up. The transom is not in line with the loading so it is not a pure shear. There is no cracking around it. What I am thinking about doing is adding some more thickness for stiffness to the interior of the transom with the load off the back stay next time I have her out. Any comment on that and any other ideas would be appreciated.

Good Winds,
DaveM
s/v DAMWEGAS

[jimgolding]

I looked on Yachtworld and saw some O'Day 35s, which seem to have a single backstay and a reverse transom. I have a Morgan 32, which has a slight reverse transom and split backstays. Even though the transom angles inboard, the transom does not point to the masthead. The chainplate, however, extends above the transom, and is bent inboard (as was the chainplate I saw on the ODay on Yachtworld) at the point where the chainplate reaches the top of the transom. On my boat, this bend makes the chainplate line up exactly with the backstay as it reaches the transom.

I think this bend in the chainplate helps prevent oil-canning of the transom. When I replaced these chainplates, a machine shop made replacements which included the bend, but the old ones had the correct bend, too, so the new ones of course came out correctly.

Jim