How to Beef Up a Transom on Pontoon Boat
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Topic: Custom transom Posted: 08/28/2012 at 9:30pm
Ok I've found a guy via a jonboat forum that lives about 30mins from me, he did an awesome job on his jonboat rebuild and did a ton of fab work to it...we have talked a bit and I think I'm going to give him a shot at the transom I'll be building on my future 3rd toon. He had a couple questions for me like what thickness plate I'll want and what size bracing I'll need.....here's how I plan on doing it unless y'all have different opinions?
I also seen this at the boat show, it's open on top and you can see the bracing
I'm going with at least a 150 but I'm considering a 225 also what is yalls opinions on this????
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Post Options Thanks(0) QuoteReply Posted: 08/30/2012 at 8:55amThe bottom pic is the way mine is setup. I've had no problems with the 225hp motor. Its rated for 300hp. I would look for a toon already done. (factory)
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Post Options Thanks(0) QuoteReply Posted: 08/30/2012 at 10:30amBottom pic is identical to South Bay's center transom tube, rated for up to 300HP (depending on boat). It's an open design and adds no extra flotation in the last 24" or so. The top one (mine) was a one-off custom design. I wanted as much flotation on the back as I could get, didn't want the "scootin' dog" look. In hind site I didn't need it. That boat sat almost level at rest with the 3-25" tubes and the old V4-140HP on the back. Yes, going to the V6 block would have added some weight, but not much. After dealing with the design like Dave's a lot, I realize mine was way over built. All boils down to what you want, and how much you trust your welder. Either will work great. Depending on how you set it up you might be better off buying one. And also remember new aluminum welds much better than old aluminum...again going back to what you use and how much you trust your welder.
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Post Options Thanks(0) QuoteReply Posted: 08/30/2012 at 2:40pmTy
That is why I recommended getting a new one. No matter what type or thickness of bracing material you use, you are still welding it all up to .090 material. There might also be alot of sections you cant get at if you're cutting an existing tube. Like you say. new aluminium is much easier to weld than old aluminium. Once you get up to that 200 hp mark there is a ton of torque placed on that transom area. I'm always checking mine for cracks. So far so good.
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Post Options Thanks(0) QuoteReply Posted: 08/30/2012 at 2:43pm This is what the back of your boat will look like with that 225.
Dave
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Post Options Thanks(0) QuoteReply Posted: 08/30/2012 at 6:17pmSure I would love to buy a brand new tube but y'all are about 800 miles away and it's not really in my budget as of now for a brand new one. I'm not 100% I'm going with a 225, I like the 175 zuke 4stroke also but then again I like the merc 150 4stroke to. I'm looking at a donor boat that's going to run me no more than $800 and it's on a galvanized trailer that I can sell and at least get my money back, not counting selling the noter tube and scraping the rest of the boat....I figure I might be into it for about $500 total after I sell everything else.....I still need to know what size bracing to use and what size plate to use? Ty on yours right under the rear log riser I see a weld that runs top to bottom, is that a solid plate you had put in there?
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Post Options Thanks(0) QuoteReply Posted: 08/31/2012 at 11:39am That sounds like a pretty good deal...Yes, that is a 1/4" plate baffle welded in. The extended part of my center log was rolled out of 1/8" and any additional plates welded in for the transom area were all 1/4". What you can't see is the internal gussets, and the 1" thick SOLID aluminum plate in the motor mount area. I can get some more specs for you but what you "should use" is ultimately your call
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Post Options Thanks(0) QuoteReply Posted: 08/31/2012 at 12:34pmJust to horn-in here. I worked with a guy in Salem, MO to make a "splice tube" for my boat that joins my front tri-toon log to my rear pod. I used this splice tube to hold a 75 gallon fresh water tank.
Anyway, my splice tube was a remnant for a new transom tube that he made for a friend of mine, and we had both shipped up together. I was impressed with the workmanship and apparent knowledge that this guy had regarding building transom logs. Here are some pics of his "works in progress":
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Post Options Thanks(0) QuoteReply Posted: 08/31/2012 at 5:05pmThanks Ty, I'm planning on doing mine alot like yours so any specs you can provide would be awesome....one question I have is when you look at a transom tube from the side the very rear where the motor hangs is usually a few inches shorter than the tube, how do you figure out this height? My center tube will be a 23" diameter, so does the top of the motor mount need to be 20"s since I have a 20" shaft motor? Or do I need to just measure that length on my current transom and use that number. But if I do this and change motors later it would change. Thanks sun blocker for those pics, the guy that's building it for me asked for some pics and these are very detailed.
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Post Options Thanks(0) QuoteReply Posted: 09/04/2012 at 11:57amIt should match your shaft length. I always see a lot of topics about correct motor height on pontoons, and really there isn't one. So many factors like log diameter, weight distribution, etc. But on a tri-toon those factors cant change. The cavitation plate will always be in the same place in relation to the bottom of the center toon, just as in a V hull boat. Yes, you will probably want to fine tune it with the mounting holes but locating the cavitation plate at the bottom of the center tube is a great start.
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Post Options Thanks(0) QuoteReply Posted: 09/04/2012 at 3:48pmall tubes should all have the same depth. when mounted so if u have a larger or smaller tube it should take that into calculations.
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Post Options Thanks(0) QuoteReply Posted: 09/04/2012 at 7:00pmCenter tube will be 23" the outers will be 22"
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Post Options Thanks(0) QuoteReply Posted: 09/04/2012 at 7:44pm BillyB I'm curious why you say that all tubes should be at same depth. I have read in some write ups that a center tube that is 2 to 3 inches deeper is OK or even preferable. I plan to install a center tube this winter so I'm collecting all info.
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Post Options Thanks(0) QuoteReply Posted: 09/04/2012 at 9:06pm
p3cflyr wrote: BillyB I'm curious why you say that all tubes should be at same depth. I have read in some write ups that a center tube that is 2 to 3 inches deeper is OK or even preferable. I plan to install a center tube this winter so I'm collecting all info.
X2 my plan was have the center tube larger but since it's only 1" larger I was going to make a spacer to bring it down another inch or so. Edited by MRT24 - 09/04/2012 at 11:13pm
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Post Options Thanks(0) QuoteReply Posted: 09/04/2012 at 9:58pmYep, I've read the same reports myself.
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Post Options Thanks(0) QuoteReply Posted: 09/05/2012 at 6:56amwhaat i was trying too say was the depth of the motor 20" - 25" need to be set in relation with the depth the boat in the water so if the tube are equal dia the height would be easier to calibrate im sure any center log wouuld be fine but the adjustment would be harder to set and its just my opinion .
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Post Options Thanks(0) QuoteReply Posted: 09/05/2012 at 9:05amSorry but when dealing with a tri-toon this is generally not the case. This is the typical mounting location of an outboard on a standard planing hull boat:
Just like in this picture on a tri-toon the distance from the bottom of the center tube in relation to the cavitation plate can't change, as opposed to a 2-tube pontoon where the weight & log size will drastically change the location of the cavitation plate while in the water. The sweet spot for the cavitation plate is just on top of the surface of the water while at full throttle. Because the 3 tubes might create some what of a different wake than a standard planing hull, fine tuning will be necessary, but as a general rule of thumb this is great starting point. Edited by PS-Guy - 09/05/2012 at 9:10am
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Post Options Thanks(0) QuoteReply Posted: 09/05/2012 at 9:52amThe Manitous have their center log sitting 5"+ lower than the outside logs. My center log (25") will sit a little over 4" lower than my outside logs (23"). I have it in the shop right now working on the mods so once that is complete and I have something to share I'll start a build thread.
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Post Options Thanks(0) QuoteReply Posted: 09/05/2012 at 10:19am I would be adding a 23 wide by 25 high U shaped center log to a pair of 19 wide by 23 high originals. It would include a welded in (fabricated) motor mount similar to the ones at the beginning of this thread. My goal is better weight support and more stable smoother ride. I don't expect any significant speed increase. Edited by p3cflyr - 09/05/2012 at 10:25am
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Source: http://www.pontoonboatforum.com/custom-transom_topic7675.html
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