Hi Guys,I've got a 24' toon w/ an '89 120 Evinrude. My plan is to add a third tube. The new 24' tube has some rub thru damage in the side of one section. My plan is to cut a 3-4'section out of the center of the damaged tube and re-weld. This will result in the center tube being a foot or two aft of the other noses once it is mounted, forward of the foot. All the tri toons I've seen have the center tube shifted forward.Does anyone think I'm headed for trouble?I look forward to having you guys share your thoughts on this topic, as I have learned a lot from reading many other threads.Thanks,Hollowoods
I went through this same discussion with a welder friend of mine who works on toons and replaces logs all the time. He also adds 3rd logs. You are right on track the way you want to do it. The only thing I would say is that I don't know how being aft of the other logs will affect things. I would have him mount the log so that the nose is just ahead of the existing logs. Being a little short in the rear will not hurt a bit. You will still gain the lift you're after, even if the log is forward of the transom by a few feet. On my 20'er, he was going to mount a 15-16' log, or even a little shorter, one foot in front of the other logs and let the rear of the log sit about 3' from the beginning of the transom. He said that was the way to go. You do not want it to block water flow to the transom. If your toon is built like mine, the transom mounting protrudes forward of the rear of the boat by about 3'. This means in my case, if I put a 16' log in the middle and let the front extend 1 foot in front of the existing logs, the rear of the log will be 2-3 feet in front of the transom where it begins at the stern. This is good! Even extending it a bit further in the front would be better for water flow to the transom. Remember, the prop has to have unobstructed water flow to it or bad things will happen. Have him mount it 6"-1' in front of the others and it will work out fine.
Hi Hollowoods, heres what I have found by trial and error on this setup. The addition of the third tube does need to be equal or forward of the two outside tubes. Reason is, the inner wake from the two outer tubes will come together in the path of the third tube thus creating as much or more water pressure for the tube to part, hence creating more drag, also the rear of the tube needs to be 3 to 4 feet in front of the leading edge of the lower unit, otherwise it will push the water down somewhat allowing the lower unit to cavitate. Or the tube can be placed directly in front of the lower unit, but the engine will have to be lowered some, thus creating a little more drag. Hope this is easy to understand, I had to move mine once to make it work correctly. Hope this helps.Wayne
Thanks for the feedback guys. The other reason I needed to cheat back a little is that I had built a set of steps that stows beneath the front deck.I need to notch out the top of the log to go under the step frame. Even after notching, the tip of the center log can only be mounted a foot back of the others. My other option would be to cut the step frame out and re design some 'dogworthy' steps.The turbulence issues rickdb1boat pointed out, I had not thought about, therefore I think cutting the stair frame out will be my first task. This is also a relief in that I won't have notch and re-weld top of the new log.Thanks for the brainpower.
Hollowoods, could you possibly send me a pic of your dog step set-up? I have three that go with me, and getting them back on board is a real pain!Sorry about going off topic :o bandb16@comcast.net
Interesting thread. What are the merits of doing this modification? How will it effect stability, speed, handling, economy, trim etc?Where does one purchase tubes? I'd be grateful for any links that can get me up to speed on this...
I'll post the improvements once I've completed the transformation.Currently W/ double cupped 13 pitch prop, WOT is 5500 rpm +~- 25 mph. At almost any speed, water washes over the logs from the inside out and the splashing underneath totally soaks the underside of deck. Dragging the cross members thru that amount of water cannot help but be horribly inefficient. My hope is to gain a little lift, whereby taking the cross members slapping of the spray out of the equation. Theoretically also the spray from the outside logs will be immediately knocked down by the center log.New log = lift + baffle = higher mph + more efficiency.More later. . .
Also, you might try "Panning" the bottom of the crossmembers with 16 or 18 gauge sheetmetal before instaling the 3rd log. This will stop the slapping of the water on the crossmembers and may even afford a little more speed in the choppy water. Not hard to do if you do it in 3 sections and use self-tapping screws to attach it to the crossmembers. Others have tried it and claim good results! I'm gonna do it in the spring. Just make sure you have all your wiring and such, tucked up and anything else you may want to run in the crossmembers done before you do this.
Thanks for the panning tip, Rick. The extra expense of sheet metal is not in the budget at this time for this project. The new log is not even in the budget, but I have sold my wife on the concept and with some trading, will be able to get it for a song.My thoughts on the panning: Logs are 22" diameter, x3=66". With the boat @ 96" wide this works out to 15" between logs. I'm hoping that the extra lift will keep the X members up out of all but the roughest of seas. If, once the new log is in place, I observe X member involvement, maybe I can convince my wife to let me spend more $ on it. Then what I would like to do would be to fab some channel stock that would keep the spray off the top of the logs too.
Got the 'new' log Sat. Cut 58" section out by first marking with laser then using a skillsaw to make cuts. Aligned, tacked and welded. Filled with 2lbs air, found leaks, drained air and re-welded. More air, more leaks. Will cut weld out and start over tomorrow. After talking to a local smart guy I have learned: Wire brush must be Stainless. Conventional wire brush actually deposits impurities on the surface. Best hope for an air tight weld is perfectly clean surface.Also he suggested rolling and tacking a piece of flat aluminum inside (half and half) under the joint. This I can do very easily by cutting a ring off of the 58" log scrap. Sure do wish I had thought of that earlier. The double thickness of material will make lineup a snap & let me be a little less worried about burning thru while running the bead.More later.
Glad to here you're making progress. Let us know how it goes. I sure am curious! Good Luck,rickdb1@earthlink.net If you care to share anything helpful or just want to discuss it.
Adding third pontoon setup question.
I've got a 24' toon w/ an '89 120 Evinrude. My plan is to add a third tube. The new 24' tube has some rub thru damage in the side of one section. My plan is to cut a 3-4'section out of the center of the damaged tube and re-weld. This will result in the center tube being a foot or two aft of the other noses once it is mounted, forward of the foot. 
Linear Mode
