My transon is beefed up with an aluminum plate that wraps around the top. Are any of you that have run big motors using any internal structural members to stiffen the transom? I think that Daniel's tow pylon ties into the lower motor mounts which is a good idea. I also designed a fairly shallow splashwell to help carry some of the loads into the deck. jim
This is actually the next thing I need to address on my project - the aluminum transom and engine mounting plates. So... I'm obviously very interested in any advice members have in this area - what they should look like, what size, what thickness, where to purchase them or have them made, etc. I can buy some aircraft aluminum - aircraftspruce is a good source - but I'm not sure what guage aluminum I need or what the dimentions should be. Greg? Dynebob?
Mark, I would use 6061T6 or similiar. It needs to go to the top, but I would not wrap it like mine. Mine is too stiff. I would think 3/16 is enough and it should extend out past the stern eyes and below the motor mount. I would put it inside and out if you can. I have seen stainless used, but I think that is too heavy. You could also tie the base of the pylon to the top motor mount to help relieve pylon loads. I am interested in hearing from some club drivers that have actually done this. jim
This is an interesting topic. John (Dyna-Ski in WI) does not like plates to be used for extra support as if the plates are stiff enough to really be strong, they will pinpoint the stress on the outer edges of the plates and in fact I have seen a couple relatively new triples that have cracks right where the plates end, and not small cosmetic cracks. He builds all the new boats with a 3" thick transom and can add that transom to any boat that needs a transom repair. As far as structural bracing, I talked to an engineer at Skeeter when they came out with their all composite transom with an aluminum knee brace that was tied to the stringers. He said it took them 3 yrs of testing to reinforce all the areas where this type of bracing spread the pressure to. If your transom is sound, you should not need any extra bracing. On our triple we added a 1x2 aluminum bar inside the splashwell to attach our pulling rings to. So far so good but I can definitely see that the stress is transferred out to the corners. The initial construction of the boat has everything to do with how well it will hold up. Honestly I have never seen a transom on a single engine dyne have a problem because of the power of the motor. It has always been from rotten wood.
We've never really gotten real deep into studying the effects of running with and without transom stiffeners, but I believe both of our multi's do have some sort of plate on both the inside and outside. One we have 1/2" thick aluminum plates, and the other, I believe is 1/8" stainless plates. If I were to do it myself, I would stick with aluminum. Not neccesarily for the weight, but more for the ease of working with it. Stainless is stronger and stiffer, so you can get by with a thinner piece, therefore making the weight fairly similar. But if you have ever tried to drill a hole for the motor mount bolts with a hand drill through stainless, you would change your mind quickly to preffering aluminum. Of course, if you have a machine shop put the holes in, it's not quite so bad. You just have to figure out the correct spacing and location.
Agreed, Stainless is too heavy, especially if you go to a gauge that is substantial. I used aluminum plates on both sides. Sorry I do not recall the gauge, but I do know it is plenty thick. I bolted them together with some large stainless bolts with nylock nuts. I had the plates manufactured in Gilberts, IL. A place called Harmony Sheet Metal. YOu see their business as you are driving on I 90 past Elgin going to Rockford. They did all of my diamond tread plate, and my stainless steel mirror bracket. They are very fast, and reasonable on their pricing. I just gave them the dimensions I needed and bam! Done! I then had the bracket, my pylon, and some other pieces either polished or chromed by a good friend that has a polishing business in Schaumburg. He is the best. He is located just down the block from the Seville off of Barrington Road. His name is Dave Froehlich, cell is (847) 544-1612. Tell him that I referred you. He is probably swamped with a lot of show cars, Harleys, and sport bikes right now so I would get whatever you want done to him now. I ran the plates past the drain hole down to the bottom of the hull. It added a lot of rigidity to the transom. With you using a 225, I would definately not "hedge" on the plates.
There you go Mark, clear as mud. I do think mine is too stiff and transfers too much load and concentrates it where the plate ends. That is why I do not recommend that the plate be wrapped around the top of the transom like mine. jim
Great stuff. Thanks, everyone. I see that Greg's (now Bob's) boat doesn't wrap over the transom but it looks like a separate transom "cap" is on there. I was concerned that if I put a cap on the top of the transom the motor mount holes won't line up. Yet I'd like to cover the top of the transom if for no other reason than to help keep water out should the seam open at all where the hull meats the deck (i.e. the top of the transom). Any thoughts on this? I can get the measurements from Greg's boat. I'll talk to Bob. In fact, I think he already gave them to me in an E-Mail that I saved. I'll probably have my neighbor do the metal work, since that is what his company does. He also offered to have his people polish the pole, so if they will do that gratis that would be my first choice. I'm not sure I understand what everyone is talking about with respect to the idea of joining the base of the tow pole to the engine mounting bolts. I can't picture that. Can someone just explain that part in a bit more detail? Thanks, everyone!
Mark, That is probably not necessary from what the team drivers say. When ski loads are applied to a pole like yours it trys to push the base of the pole toward the front of the boat. When motor loads are applied to the transom it tries to push the top motor mounts toward the back. If the base of the pole is connected to the upper mounts (it would take two pieces) the loads tend to cancel each other out. It helps to keep the transom from flexing and relieves some of the load at the base of the pole. jim
