21' party deck to light weight fishing boat


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Feb 3, 2022
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Harrisburg Illinois
Hey guys
this is my first post and I hope you guys get as excited about this as I am.
I am slowly refitting a 21' aluminum tracker party deck (not pontoon) to a fishing boat better set up for these shallow Illinois waters. It currently has the deck and everything except for the engine removed.
The boat came with super heavy 5/8ths ply wood that was probably 50% water. It also had a fair bit of floatation installed that held plenty of water also. I have removed the flotation and decking. I am going to reinstall the pour in foam but I will be installing water channels under the foam to help the water flow towards the bilge pump instead of sitting and getting soaked up by the new foam.
I am then replacng the plywood with the lightest gauge aluminum flooring I can but I have no idea what thickness I can get away with.
The stringers are 16" apart and I will be adding 1 in the middle and 1 on each far side(front to back) and I will be adding cross bracing (left to right) every foot. I have read about everything I can find about this and believe that I pretty much have It down to 0.063 or 0.08 thick 5052-H32 sheets.
deck bracing.jpgI dunno???

I am thinking Ill drill holes in the sheet and tack welding (spool gun) every 6 inches along the stringers and crossways along the ribs.
The problem with this method is I cant install it over eps foam. I like the foam idea because I bet it would quiet down the wave smacking but my brain says tack weld for strength...

can 0.063 span across my 16" x 12" openings?
should I tack weld or install over 1" eps pink foam with screws?

thank you

PS the super heavy 4.3 mercruiser will be replaced with twin yamaha 701 2 strokes and jet drives in the future. that will save me about 500 pounds and give me about 150 HP total in a boat that should total about 1200lbs
My two cents: To make life a lot easier should you ever have to access under the floor, screws instead of welds, and sheet or blocks instead of pour in foam. To save $$$ use 1/2 ply instead of alum.

Whatever you decide that is going to be a nice boat when you are finished.
Thanks for the reply! I am really trying to stay away from wood. It is a lot cheaper and not using it is the reason this project is going at a slower pace.(money). I usually try to get my projects done quickly in fear of them getting put on blocks behing the shed and forgotten about. Wood has merit but at the moment i am ok with the slower build pace in favor of aluminum and weight savings. This boat was twice the weight it should have been when delivered from factory

Another thought was to install the bracing and glue with 5200, eps pink board to the bracing/stringers and then glue the aluminum sheeting to it with a few well placed screws. Also install hatches in maintenance prone areas. This should be less permanent than the welds but 5200 is pretty tough stuff.

Wood does look better and better the closer we get to summer.

Thanks for the idea and compliment!
Do you plan on carpeting the aluminum? straight metal will get hot. carpet will stay cooler, and wood will also stay cooler. if you are running all of that bracing you can go with 1/2inch, seal it, and it's easier to hatch, carpet and repair/access. Once its decked, in my experience you will have plenty of strength and rigidness
thefirstbert said:
Wood does look better and better the closer we get to summer.

If you don't already know.......whatever you do, DO NOT install pressure treated wood onto aluminum. The chemicals tend to corrode aluminum over time. Modern chemistry may have negated that, but I would still be leery.

I am actually kicking around the idea of spraying it with white polyurea and antislip grit. I have used it a few times on other projects and really like how it performs. I always have a spare pint or 2 and by keeping all of my projects the same color, color matching my repairs have been pretty straight forward. Not sure yet though. I personally would choose anything over carpet though. It has never been a good choice for how i use my boats. Looks good though but its just not for me.


Thanks for the heads up. I know they have changed the PT chemistry in the last decade or so but I still dont trust it or know if its still a problem with aluminum. Like you said, better to stay away until others start reporting long term success.

The wife and I sat down and figuered up our finances last night. I will be ordering aluminum bracing and sheets in just a few paychecks from now. Atleast the bracing...

Im going to go with AL sheet over foam. I like what everyone is reporting with that method

I am also thinking about oxyhydrogen for welding the brackets instead of spool gun due to the malleability of the joint afterwards. Spoolgun can leave a brittle weld less forgiving to flex. Im not sure about that yet. No room in the budget for a tig and I do my own welds...

I do know that in about 3 weeks this project is getting kicked back into gear. I hope to have the aluminum done before april. I might wait till next winter to install the jet drives.

Anyone have seeds for a money tree?

Anyone have any experience with a cheap camera that will provide decent video for youtube?
Coming up on a year. Did you ever start?
Most cell phones now give good HD video in a pinch.

1/2" plywood will easily give you a decade or more of use if you take the time to waterproof it first, particularly the edges, as long as you keep the bilge dry. Blocks of foam, so there is air space underneath will help it last even longer.
I agree with the sealed plywood, one thing that wasnt mentioned is that an aluminum floor would be very slippery !!! What ever you use, use screws, so it can be removed if needed. If using a good 1/2" plywood you can open up your spacing to at least 16" x16" without a problem. On one of my tinnie mods I used 5 ply 5/8" plywood and spanned 24" with no flex and I weigh 200 lbs. At one point I went almost 36" and could just notice a little flexing when my weight was on it. Cheaper to go slightly thicker on your plywood and spend less on your expensive aluminum framework.
It really shouldn't have been too expensive. To me, that looks like 4 sheets of 1/2" plywood, a gallon of Thompson's wood preserver, carpet or vinyl flooring and get back on the water!

Over complicating projects often means they never happen.
Fortunately for me, when I was younger I worked with older techs who had a way with words.

They would say stuff like, "Son, we are already making it better than factory, and that lasted 25 years. This should last 40. Why on earth are you trying to turn this into a science project?"

And, "Something you need to remember... You never get time back. Once it's gone, it's gone. Don't throw it away. As you get older, you'll appreciate what I'm trying to tell you."

And now that I'm older, I DO. So I try to look at a project and decide how much time and money I want to put into it before I even buy it. Often, the end value won't be enough to justify it. Sometimes, I could buy the same boat with a good motor, in good condition for the same or less than the money and time of fixing it up. So I shop very carefully nowadays!

You never get time back, so use it wisely.
Last edited:
Going back to this Party Deck boat...
What was the mistake made with the boat before? I see 2 primary things:

1. They did not seal their plywood and it sopped up a ton of water.
2. They either did not seal around the deck or the bilge held a lot of water and it saturated the foam.

For #1, you simply need well-sealed decking. With support 16" O.C. I would use 4-ply or better 1/2" plywood and seal it with epoxy or resin. If I really liked the boat, I would also lay 3/4 oz glass matt on the top and bottom of the plywood. That has the benefit of making the floor MUCH stronger and even more impervious to rot. Either way, spend time sealing EVERY fastener carefully. Pre-drill, saturate with resin, drive the fastener.

For #2, Find where the water came from. Fix any leaks, bad pump hoses or whatever. Then, after you lay the new floor, seal 100 percent of the floor perimeter to the hull of the boat. Make sure the floor does not touch the hull at any point. and then use a sealant. You could use a number of products, but I would avoid silicone.

The idea is if you never get water in your bilge, your foam will never get saturated.

Thinking it out isn't hard. A few details makes the difference between doing a fair job and an excellent job.

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