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boat lift bunks

I am about to convert my lift as well from V-hull to Tritoon for a 23RSB. I want to have as low of a profile as possible due to seasonal low water. (currently my lift is high and dry due to the scheduled draw down of our lake this year...most years have plenty of water year round but it can be shallow)

My Bennington Dealer suggested three 2x10s that are 16 ft long in treated lumber (MCA treated - so it'll be safe with aluminum), each running under a toon. I do not plan on covering them with carpet but may stain or water treat them. I plan to use carriage bolts through the existing aluminum I-beams, counter sinking them if possible.

Does this sound reasonable? Are 16 foot long bunks required? (I see many of you use shorter bunks.) I know Team Bennington suggests that all of the toon support points be supported, but that doesn't seem possible on a 23 ft long toon. Attached is a photo of my current lift. The cradles are 9 feet apart. If I use 16 ft long bunks, I will have 3.5 ft of bunk extended in front and behind the cradles. (and 7 ft of pontoon not directly supported). Should I place the bunks spaced evenly so the same length of bunk hangs over the back and front of the cradles? Thank you in advance!
 

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I'll have to figure mine out too. We just bought our house and this is the lift that came with it. The previous owner had a 30 ft. v hull on it. It's rated for 10,000 lbs. We'll be buying a 25QX next summer.
Any suggestions on making it tri toon capable would be welcomed.

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I support my Tri toon from under the deck, not from under the toons. It’s a shore station lift. I would think you could get similar racks made for your lift. Doing it this way gives you the most amount of low water clearance, as you can set the height so there is, say, 1/4” gap between the top of your lift beam and the bottom of the toon.
 
Here is how I had my lift modified, copying CWAG's simple style of 3 parallel flat planks. Works great. I had mine clad with bunk wrap since the wood is the classic pressure treated, which would be bad on the aluminum.

The planks are 3 x 10 x 16. The rear of the pontoons are just on the end of the plank, and the front of the toons (where there is very little weight) hang over the front of the planks. No issues.

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JTaylor said:
Here is how I had my lift modified, copying CWAG's simple style of 3 parallel flat planks. Works great. I had mine clad with bunk wrap since the wood is the classic pressure treated, which would be bad on the aluminum.

The planks are 3 x 10 x 16. The rear of the pontoons are just on the end of the plank, and the front of the toons (where there is very little weight) hang over the front of the planks. No issues.

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I'm new to this boat lift thing, so, are you saying a 3x10x16 board will line up and support a 5,000 lb boat?
 
We bought our 2007 tritoon (2575RL I/O) a year ago.
During that time, I have felt some alarm at the discussions here about boat lifts... particularly where I saw comments indicating that the warranty could be voided if lifted improperly, such as with straps.

My brother kept the boat in his boathouse lifted with two large straps, one going under the big engine nacelle. The boat only had 110 hours on it, so it didn't get lifted much.

It never occurred to me this could be a problem, particularly since his dealer delivered the boat to him and serviced it every year. So far, I'm not seeing any problems that are obvious.

What should I look for in the way of early indicators of a problem?
 
For 25 years, I built decks and docks as a side hustle. Maybe I'm missing something, but I don't see much support for those 16 long planks laid "on the flat" (not stood up like a typical floor joist). A 2 x 10 in a vertical orientation will span 8 - 10 feet easily. But lay it "on the flat" and it will sag under its own weight over about an 8 foot span (rough estimate). I know you guys are talking about nominal 3 x 10's, but they need support too.

If the distance between your cradles is 9 feet or more, those 3 x 10's aren't doing much supporting.
 
Fix marine supply 239-540-2971. They sell cat bunks, 10'' wide 12 16 20 ft long. fixmarinesupply.com They do not show them on the web site. They are pricey but very nice.
 
sunedog said:
For 25 years, I built decks and docks as a side hustle. Maybe I'm missing something, but I don't see much support for those 16 long planks laid "on the flat" (not stood up like a typical floor joist). A 2 x 10 in a vertical orientation will span 8 - 10 feet easily. But lay it "on the flat" and it will sag under its own weight over about an 8 foot span (rough estimate). I know you guys are talking about nominal 3 x 10's, but they need support too.

If the distance between your cradles is 9 feet or more, those 3 x 10's aren't doing much supporting.
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I see your point. I am also on Lake Murray. Do you know if there is a local source for aluminum bunks? What method would you suggest to retrofit my lift to support the toons?
 
Like Joel14 mine lifts from under the deck. I called Bennington and they said there is no issue with this configuration. Besides great low water clearance, if you set up the supports well, they guide you right onto the lift without needing the outside guides. I also have a Shore Station. You can check out their website for what this looks like. Can’t imagine it can’t be duplicated with any hoist.
 
For Shorestation they are call “ toonrails” that lift the boat. If adjusted well, you don’t need any additional guideposts.
 
Tomc said:
For Shorestation they are call “ toonrails” that lift the boat. If adjusted well, you don’t need any additional guideposts.
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I like that, but I'm not sure that would work with my current lift. The Shorestation lift appears to be a square cradle, and mine is two separate cradles...might not be secure enough. I'll call them tomorrow to see if it will work on my Boat Lift US lift. Thank you -
 
Here's another perspective of our lift, with an I beam under the center plank. So much of the boat's weight is on the back where the rear cross beam is. We've been using this for a couple years with no issues.

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Chris A -- I don't know of a source locally, but a friend of mine works for Agnew Docks and I bet they have a solution. You may try calling them and asking for Nathan. Tell him John and Crystal said hi.

JTaylor -- That I-beam is the ticket. Looks very stout.
 
Chris--I have a lift like yours and it was supporting a 24 foot Sea-Ray deck boat. I sold that boat and bought a 24 foot bennington tri pontoon. Here is a picture of the lift changed over to a tri pontoon lift. Total was $1500.00 to have lift pulled from dock to ramp and loaded on trailer, refitted with new bunks and then replaced in slip with new bolt fitting drilled.
 

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I modified mine with (aluminum safe) treated lumber like many of you on this forum. My cradles are 9 feet apart and offer very good support. I will use the previous V-hull aluminum bunks on the outside of my pvc guides, flat against the cradles, as walking planks, which will also stiffen up the whole structure. If I feel it isn't sufficient I can always buy aluminum bunks later.
(My local dealer, whom I trust, validated this setup for my lift and boat.) Thank you for all of your suggestions.
 
I'm a bit confused about the bunks on these lifts. I'm trying to retrofit my lift for a Tritoon. The bunks on there now are 20ft long. The manufacturer said I would need 4 more bunks at a cost of $750.00 each plus shipping. He said they are not aluminum but wood. Are they trying to sell me a 20ft pressure board for $750.00 that I can get at Home Depot for $20.00?
This is where the confusion comes in. I'll call the manufacturer tomorrow for more info but thought the knowledge here would be helpful too.
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That seems excessive. The frame you have on that lift looks pretty stout, with a cross beam at mid length. If all three cross members are at the same level (plane), I would just lay 2x12’s on the frame, centered under each toon. If there is concern that the flat board won’t give enough support between each cross member, then first bolt a steel or aluminum channel to the cross members, and then screw the 2x to the channel.
 
I used 2x12's then wrap them with piling wrap. the picture does not show the two supports i put under the bunks parallel with the cradle. Works great. IMG_0740.jpg
 
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