I want to install a transom plate on my 1989 Hydrodyne 20 Comp powered by a single 1989 Yamaha V6 200. Both boat and motor are original just like when I picked up the rig from the Spencerville School House factory. I am looking for information on the best methods to do this work. My questions are: size of plate?, thickness of plate?, what grade of stainless steel to use?, How many bolts for attaching?, and any other helpful hints or suggestions for this job.
I would suggest that you use aluminum. It is much lighter and will accomplish the same objective. I will endeavor to measure the size and thickness of mine with a micrometer and post the number. I have one large plate on the back of the transom, and two smaller plates on the inside - one in the splash well and one below the splash well. I have attached a couple of pictures. Good luck. Markbano
Thanks for the suggestions. You are right aluminum would be the better choice. When I bought a 74 boat with an oversize hp motor the dealer would not sell it unless a plate was installed. When the dealer had it done the fabricator put a 90 degree bend two inches wide on the top that went over the transom . The bend fit nicely in the motor bracket and looked like it would add to the strength of the plate itself. The two inside smaller plates also look good to me. I appreciate your helpful commenets and pictures. Dennis
I would do it like Mark's. Don't flange it because it will interfere with the motor mounting. It also makes the transom very stiff behind the plate making a stress riser at the edge of the plate. I know because mine is done that way The inside plates coincide with the motor mounting bolts. Aluminum is also better because it is much easier to drill. jim
If you plan on having a lip at the top, before doing so, make sure your transom is flat. I believe some of them have a slight arc in them, which would make a stiff flat plate less than desirable.
I can tell you that even the small, non-structural angle piece that goes along the top of my transom interfered with efforts to mount the engine at the lowest position - so you wil not want a larger, thicker aluminum plate going over the top of the transom. The weight of the motor rests entirely on the mounting bolts. These big engines - even at the lowest height setting - do not rest on top of the transom (as smaller outboard engines do). Thus, there is no benefit to having a large structural piece on top of the transom. It will just force you to mount the engine higher than you want. I will try to get you a spec on the plates. You might do a search on the forum, too, because I think there were posts about this at the time I was installing the plates. Markbano
The new Dyna-Ski boats we build don't have any metal or aluminum plates on the transom. The transom on a new style Dyna-Ski is a little over 3" thick for a reason. After two seasons of use the Badgerland 20' Dyna-Ski boat with three 250 HO Evinrude E-Tec Motors has no cracks. This is the second season for the Must Skis triple big block boat. No cracks here either.
Thanks to everyone who replied to my request. My plan now is to install a 20" wide by 15" deep 1/4" flat aluminum plate on the back with one 20' by 4' inside the splash well. I will do a lower inside plate if I can get to the area. This size plate will allow me to reinforce the transom without disturbing the two attached step platforms. I would have posted some photos but I just upgraded to a new computer, operating system, and phote application and I have not figured it all out yet. I'll post some pictures under Hydrodyne 20 when I can.
