Tritoon Add-on to a 1976 Starlite

[Jonezy Hick]

So after 5 years of cruising around on my old boat and checking craigslist I found a "cheap" and local third tube to add on to my old pontoon boat. I purchased a 23' and 23" diameter with a transom and 38 gallon fuel tank. I am planning on adding the center tube about 12-16" back from the other tubes. I plan of beefing up the structural soundness to compensate for the extra tube by adding some more ribs to the deck.

Since this will be my first time adding a third tube to a pontoon boat I am hoping to tap into you'alls vast knowledge and not make stupid mistakes and hopefully have a smooth install. I will be pulling up the deck and replacing it, but that is another post.

Any help will be greatly appreciated

-Jonezy

P.S. I have access to a shop with tig welder, chain hoists, tools, and a backyard mechanic degree.

 

[ahicks]

Sounds like a great project. With your degree, you shouldn't have much trouble at all. With the deck off, things are pretty straight forward I would think. Not sure of your thinking on the extra cross members. With the extra pontoon providing way more support to the existing, and the engine hung on the back of the center 'toon, I would think anything that's been working this long would work fine.

Not keen on the gas tank plan myself. Putting gas in that center toon would be like dragging water around in a leaking pontoon. You're subtracting from available flotation and adding weight. That's me and how I use my boat though. -Al

 

[Scott Danforth]

nothing wrong with the fuel tank in the center toon. same effect on displacement as carrying it above, however just frees up deck space

 

[Jonezy Hick]

ahicks, the gas tank is built into the tube.

It looks like a straight forward project, but I have a few questions:

1. Should I bolt or weld the tube?
2. Is 12-15" behind the current tubes sufficient or should I go with even with the current tubes?
3. How do I find out the horse power rating on the transom?
4. Once all this is finished how do I update my loading and capacity plate?

-Jonezy

 

[Scott Danforth]

1. I would bolt the M brackets to your structure

depends, what is the length of your current tubes vs the new tube

for 3 & 4, you have to start digging into the ABYC standards on 'toons and get the USCG involved

you are looking for ABYC H35

here is a link to an on-line version I found
https://people.cs.uchicago.edu/~luitien/h-35.html

specifically this page https://people.cs.uchicago.edu/~luitien/h-35.html#3

https://abycinc.org/page/standards

http://newboatbuilders.com/pages/pontoons.html

 

[Jonezy Hick]

Thanks Scott!

I know I am getting into a lot of detail, but I do not want to do this twice or have the tube fall off while
I have the whole family on board, haha!

-should the bolts be put on with split washers, threat lock or nylock?
-the old tubes are 26' 8" overall length and the new is 23'

looks like the ABYC H35 is going to be like going to the DMV, I CAN"T WAIT!!! It looks fairly straight forward though.

-Jonezy

 

[ahicks]

As far as fasteners, just duplicate what the rest of the boat has going on.

As far center tube set back, I would be looking more at what you have going on in the back of the boat and let the front take care of itself. A lot of what you have going on in the back will be about how much power you plan on, and what that plan is going to weigh.

Custom boats don't need USCG approval. You have become the manf. of a custom boat. You should however, be familiar with "common practices" used in the construction of boats. For that, use your "degree" to observe how the rest of the boat is assembled. Duplicating that should leave you with a sea worthy boat no governing/sanctioning body will want to get involved with.

My earlier comment regarding the gas tank was regarding the capacity. I live on a lake with a 24' 'toon powered by a 90hp Honda. 38 gallons of fuel would be like a 3 year supply of fuel based on our usage/gas consumption over the last couple of seasons. For that reason, I believe that tank is at least twice the size it needs to be.

 

[Scott Danforth]

split washer have no business being used anywhere. from a bolted joint standpoint, its a failure waiting to happen. they were designed in the 20's to hold sheet metal on vehicles, however by the 40's fastener technology made them obsolete.

if you need locking, a large flat washer or a belville washer, and nylocks torqued to the right spec.

 

[Jonezy Hick]

ahicks,

The back of the boat has my batteries, fuel, and an old 140 hp Johnson two stroke. Mid is usually filled with people and coolers and the front usually has a dog or two. I can move the batteries around (cooler and people too if need be) and the fuel tank is now in a fixed position. I am thinking about bolting on the pontoons just to see how it floats in the water and then welding them to the frame like the other side tubes once I find the sweet spot. But I could use a little advice on that sweet spot. I do not plan on this being a fast boat mostly a slow and low cruiser, but I would not mind getting back to the docks at dusk a little quicker.

Eventually I would like to put a 115 Yamaha or maybe something a little bigger, but the department of war and finance might have something to say about that :becky:

Scott,

Looks like I will eventually be welding the center tube on and bypassing the whole bolt/nut debate. There is a lot of fasteners on this old gal that have to be looked after and I have replaced most of the nuts with nylok fasteners, but there is always something rattling loose.

Thanks guys for the responses. Its given me some confidence to get this project going with out fear of paddling towards my center tube and outboard in the middle of the lake, haha

-Jonezy

 

[ahicks]

Not crazy about the welding idea here. That boat is constantly flexing as it moves through the water (while dealing with waves and wakes), and flexing is something a weld doesn't take real kindly to.

I would have a tendency toward mounting the transom of the center tube about even with the back of the existing tubes. Thinking that should give you the max flotation possible. The engine you are using is not exactly a lightweight, and with that and the other "stuff" that generally accumulates in the back of a boat, thinking you could use all the flotation you can get.

 

[Jonezy Hick]

The stock pontoons are welded onto the cross members, but I like the bolt/washer/nylok combo idea better.

That engine is a HAUS! I am not looking forward to transferring it to the new transom. :dizzy:

 

[ahicks]

If you or a buddy has an engine lift, normally used for pulling engines from a car/truck, those work pretty good. You do need to have your wits about you, and no hurry!

Lucky enough to have a small tractor with a loader on it here, and I'm STILL pretty careful!

 

[NYBo]

What are you trying to accomplish with this project?

 

[Jonezy Hick]

My goal it to increase the carrying capacity of my old pontoon boat.

 

[ahicks]

All due respect, but swapping that 140 for something like a 50 or even 65 would raise the back of that boat quite a bit if that's your primary objective.

 

[hvymtl939]

Your outer toons are welded on? First I've heard of that. All I've seen are bolted to the cross channels. That is how we will add on our middle log. Does the center log have lifting strakes? I assume your toon is old enough the outer logs are 19" diameter?

 

[Jonezy Hick]

ahicks, I will eventually be getting a 90-115hp outboard, but I could not pass up the price of the center tube ($800) and a used four stroke is in the $3000 ish range. Finding a used outboard is easy, but finding a center tube under $1000 is like finding a unicorn mermaid. My transom needed to be rebuilt and I have nose dived a few times when the wind comes up on the lake or a large boat goes by even with only 4 people on the boat, so I thought I would fix the buoyancy issue before I re-power.

hvymtl939, This is my first pontoon boat, but I have noticed all other pontoons have bolted on tubes. The center log has lifting strakes, built in fuel tank and transom. I do not plan of getting up on a plane (I would need a lot more HP). Yes, my tubes are 19" diameter hence the weak loading capacity.

-Jonezy

 

[5150abf]

I have built pontoon boats for 32 years,specifically tubes and rails, spent 20 years at Bennington and am currently the weld shop manager for Barletta boats.

Do not weld the tube to the frame , especially the center tube with all the vibration from the engine.

Aluminum cracks and you would have to contently inspect all the welds for cracking, a broken weld fails 100%, a lose bolt still has holding power.

I would run the center tube even or just behind the outboard tubes and let the front fall where it does.

I would think you would want to watch setting it back to much as you could get a weird spray thing with the outer tubes hitting the center funny if it is back to far.

Also the farther back it is the more engine weight influences the boat, like a teeter totter, if you make one side longer it increases the weight on that side so the farther back you run the engine the more it effectively will weigh if that makes sense to you

Do you know what boat your center came from, should be easy to extrapolate the engine rating from that, I would think certainly good for 115 possibly 150.

Doing this with the deck off should be relatively easy as these things go, getting brackets and crossmembers to line up is usually the biggest obstacle.

 

[Jonezy Hick]

OK, Stainless bolts with nylok nuts to anchor the center tube. I will mount the center toon even with the existing tubes.

The center toon came from craigslist, but it looks well built (see pic), so I am not sure of the horse power rating. I will look for an ID Plate to confirm. That way I do not overload it with my 140hp hog of an outboard.

 

[5150abf]

Been welding pontoon boats for 32 years, currently the weld shop manager for Barletta Boats.

I would never weld the center tube on,, welds fail 100%, when they break a lose bolt still has holding power.

Aluminum cracks, it is just one of its properties.

Bolting would be much easier in my opinion any how and as I said, a, lose bolt will still hold the tube on, once the welds start cracking and failing you will have real issues.

You will add buoyancy with a 3rd tube but you are also adding weight and water resistance.

I would put the back of the center even with or behind the rear of the boat and let the front fall where it does