Pontoon Boat Chassis Question...

[Vulcan315]

I have a 1990 Lowe Sunbird 24' Pontoon that I'm restoring. I have everything off the chassis. I've been searching everywhere, and hope someone has some info or can make an educated quess to help me. This has the old style foam filled U-shaped pontoons. I think they used cut blocks, not the sprayed in closed cell stuff they use now. Currently, the two 24' floats (logs), the metal chassis and the framework that holds the pontoons together (all the cross-members), & the transom is weighing in at about 1000 lbs. I'm concerned the logs may have been contaminated with water in the past...though I got very little water out when I removed the drain plugs. Have any of you ever weighed the floating chassis of a similar boat size while it was torn down for rebuild?

Dave

 

[Scott Danforth]

At 1000# you are waterlogged

 

[Vulcan315]

I was kinda worried about that. I'm guessing the 24' logs would be maybe 200# each. Will remove a few pieces and try to guess at the rest. I don't think the logs could have a vacuum pulled to remove water, the structure couldn't withstand that. I wonder if the logs were vented adequately with airflow, if the bulk of the water would eventually evaporate? I don't think they're baffled inside.

Dave

 

[Vulcan315]

Still working on weight... .080" 5052 aluminum ~1.139 lb/ft. One log has about 154 sq.ft. = 175.4 lbs.. This doesn't count all the brackets and the reinforcement rib in the front. Still adding stuff. Sure seems water logged.

 

[Scott Danforth]

use an FLIR camera in the morning just as the sun is coming up it will allow you to see the cooler spots where the water is.

 

[Vulcan315]

Thanks Scott, I think I have a friend at a speed shop that has one.

These U-shaped logs with flat tops have about 154 sq ft of .080" 5052 aluminum, that would put the bare log at 175#. I found a cut away of one of them, and based on the the info there's about 120 lbs of 2lb foam inside, bringing the logs to about 295# each. Gonna try to figure out the weight of all the other stuff, Lowe doesn't seems to have the info on these 32 year old boats.

I plugged the vents, put 1psi of air in the logs and they're still holding for the last 12 hrs. Makes me wonder if water was coming in though the vents over all these years. The cam may help, still can't find out if the logs have baffles, or if they're just open boxes with a bunch of foam inside. They used thinner metal, I guess the foam would help keep them from canning.

Dave

 

[Scott Danforth]

its 32 years old

that is a lot of moist air to breath in the vents, condense into water, and start deteriorating the foam.

there is a reason that standard hollow 'toon logs are so prevalent.

yes, the foam is structural allowing for less money to be spent on aluminum sheet.

 

[Vulcan315]

I'm gonna raise the pressure a little and see if I can find a crack, was concerned about raising it much. Its not a pressure vessel and 1 psi is 2264 lbs of force against the interior. Have you pressurized logs for leak checks before?

 

[Scott Danforth]

all the time. however round tubes. 2-3 psi.

 

[Vulcan315]

Well, at 2psi I found lots of little leaks around the 72 bolts that are drilled through the flanges that hold the logs' lids to the u-shaped lower sections. The edges of the flanges are welded, but the bolt holes are common to the interior. Lowe shows a layer of sealing tape between the lid and lower section, but I guess at 32 years of age, that has deteriorated. I'm gonna pull each bolt and try to seal around those with silicone.

I weighed a sample of the z-bars and other structural parts, weighed bolts, and have extrapolated the weight to be close to 900 lbs, now...not counting the transom / trough / etc associated with the motor mount. The trough is a huge piece, fabricated from 3/16" plate aluminum, chunk of wood, etc. That might get me close to the 1000lbs I saw on the scales. Dunno, but I'm not as worried as I was.

I do see about .015" of pitting at the waterline of the .080" log metal, so I'm gonna jack it up and put a couple of coats of that marine epoxy on them.

This beast is heavy. Been a learning experience, for sure!

Dave

 

[Vulcan315]

Thanks for all the help. I removed the entire transom assembly, and it weighed 115lbs! Not reusing it, but this brought the chassis (logs and frame) weight in the ballpark for what it should be. I'm adding flotation the full width and length of the space between the logs with a simple plow up front. Dark and fresh water tanks in the center under the hull, and weighing everything to keep balance correct. Flotation on the 24x8 chassis will be a little over 14000 lbs. With those square structures @1/2 immersion, I'm way over whats needed, so I should be in good condition with the metal & foam insulated structure expected to be under 4000 lbs. Using electric propulsion just to move it around in the marina.

Dave