Subfloor question

[PunkR0ckz]

Hey everyone, I'm starting to shop around to repair and restore the boat I bought this winter, a Starcraft Offshore-V 18.
The hull and console are in great shape, that's about it; it doesn't have much left of the original "oar & rod holders" on the sidewalls or any of the flooring, or even the back panel covering the bilge pump area.
I have access to this aluminum structure, that is 50" x 50" by about 6" or so in thickness. The guy is selling these structures for 75$USD a piece.
Would it make for a decent subfloor, or would I be asking for trouble?
I might add an aluminum gas tank near the center console (yes, I want to go for a center console, not a dual console setup!) along with some ACM 1/8" panels (aluminum composite material, or basically some "plastic" with layers of aluminum on both sides)
I'm thinking all of the separators will add a bunch of strength to my ACM panels, but it'll also add a bunch of weight. If my maths are right, that'd be about 100lbs per panels and I would require 3.5
As a sidenote, I might grind off the 1x2s (or whatever they are) and use them to space apart the frames lengthwise but also to center them in the boat.
Anyway, great idea or steer away and why ?

 

[MrGiggles]

I could see it as being very handy for a deck structure, but I'm not sure why you would want to use it for the subfloor. You likely already have an aluminum subfloor structure under the current plywood, no need to reinvent the wheel.

Unless you were wanting to build a new deck with it, I think the money would be better spent on composite decking, aluminum sheet, or just plain old plywood that would work with the current structure.

Plastic certainly has it's uses, but boat flooring is not a very good one. It's not very rigid or temperature stable, needs a lot of support underneath and will tend to buckle or pull out your fasteners as it expands and contracts.

 

[PunkR0ckz]

I could see it as being very handy for a deck structure, but I'm not sure why you would want to use it for the subfloor. You likely already have an aluminum subfloor structure under the current plywood, no need to reinvent the wheel.

Unless you were wanting to build a new deck with it, I think the money would be better spent on composite decking, aluminum sheet, or just plain old plywood that would work with the current structure.

Plastic certainly has it's uses, but boat flooring is not a very good one. It's not very rigid or temperature stable, needs a lot of support underneath and will tend to buckle or pull out your fasteners as it expands and contracts.

Underneath the plywood, there are only 2 Z-shaped longitudinal pieces that are spread out pretty wide. I do not want plywood in my boat. I plan to keep it for my entire lifetime, so I want something that won't require much maintenance. I am also 350lbs 6ft3, so I need something that adds structural integrity to the floor, those 2 Z-shaped pieces with plywood is OK, but it certainly can be improved... Since I will most likely go with ACM for my floor, I know it'll require something stable, strong and with a lot of support underneath. That's why I thought those structures would be helpful, plus, at this current state in the project, I need about 4 inches of additional height for the aluminum gas tank to fit, unless I poke a hole through the plywood and allow the connections to be done on the outside, which would be ugly. I haven't rebuilt any aluminum boats yet, this would be my first one, I can't think of any other issues to be honest other than weight and it might be harder to use as its already welded and everything instead of me doing it with rivets.

 

[LDUBS]

Nice boat -- diamond in the rough! I hope you keep posting updates.

Here is my two cents and some random thoughts. If I was worried about the floor flexing, 1/8 ACM would not be my first choice. In reality, we are talking about adding 350 pounds of framing to the boat in an attempt to make a floor out of something that is thin and flexible. If you don't want plywood, go with aluminum sheet. Fancy composites, like Coosa, are impressive options and suitable to a lifetime boat. Worth a look if the sky high price is acceptable. Add support, if needed, to replace any structure lost by removing the two side consoles. If you think the spans are too great for your flooring, you can add lightweight aluminum angle as needed. To avoid the need to raise the floor so much, maybe you could put the gaso tank fittings under a seat or storage box in front of your new center console.

 

[FuzzyGrub]

FWIW: I would not raise the floor 4" for the gas tank. That can be a significant COG change. Is there a lower profile plastic tank that will suffice? I think the aluminum would promote more water condensation, too. Was the OEM a couple of portable tanks?

 

[thill]

If you have your mind set, then I hope you enjoy the project and it works well for you.

As many others state, ACM would not be my choice, for the reasons already mentioned.

Do you have access to straight aluminum sheet, without the plastic center? If so, many have made aluminum skeletons and installed sheet aluminum flooring, and they turned out. Something you might consider, if your mind isn't hard-set on the ACM sandwich material.

Adding 350 lbs of material to an aluminum boat definitely could change the dynamics of the boat, but the fun of doing YOUR own projects, is doing it YOUR way. Just be safe, and if it doesn't work out, be man enough to just fix it, rather than sell someone else a problem.

I say this, because over the years I've seen a number of people ask for advice, go against all the given advice, and when they were done, suddenly their "forever" boat got sold and now they are working on something else. Then someone pops up trying to fix a problem boat they bought, which is the same boat. I think you see what I'm getting at.

Definitely update the project as it goes along. Looking forward to seeing your progress

 

[PunkR0ckz]

If you have your mind set, then I hope you enjoy the project and it works well for you.

As many others state, ACM would not be my choice, for the reasons already mentioned.

Do you have access to straight aluminum sheet, without the plastic center? If so, many have made aluminum skeletons and installed sheet aluminum flooring, and they turned out. Something you might consider, if your mind isn't hard-set on the ACM sandwich material.

Adding 350 lbs of material to an aluminum boat definitely could change the dynamics of the boat, but the fun of doing YOUR own projects, is doing it YOUR way. Just be safe, and if it doesn't work out, be man enough to just fix it, rather than sell someone else a problem.

I say this, because over the years I've seen a number of people ask for advice, go against all the given advice, and when they were done, suddenly their "forever" boat got sold and now they are working on something else. Then someone pops up trying to fix a problem boat they bought, which is the same boat. I think you see what I'm getting at.

Definitely update the project as it goes along. Looking forward to seeing your progress

No, I am not hard set on ACM. However, I think it might be a good choice. I am a beefy boy at 350 pounds, the plastic stiffens up the aluminum, and ACM can be had for quite cheap on FB Marketplace, 3/16 aluminum is something like 200$ a sheet if I remember properly whereas ACM was about 100$... that is why I was thinking about that as an option.

No, I wouldn't see a problematic boat to someone; happened to me a few times, had to repair them and sell them at a loss because they wouldn't fit my needs perfectly over the years, but nothing in regards to the hulls/foam yet! It was always about either weight of the vessel, size of the vessel or ergonomics (selling my bass boat because I am sitting too low in it and I have serious sciatic issues...).

 

[PunkR0ckz]

FWIW: I would not raise the floor 4" for the gas tank. That can be a significant COG change. Is there a lower profile plastic tank that will suffice? I think the aluminum would promote more water condensation, too. Was the OEM a couple of portable tanks?

Most likely was 2 tanks, but I don't like that idea whatsoever. I want a spacious boat, putting 2 tanks under the transom area means I will lose valuable storage space for other things that I plan on adding. The tank actually fits under the floor, it's the fittings that don't. From what I understand, it was either custom made to be put under the back horizontal transom plate (I don't know if it has a name, the aluminum plate that is weirdly shaped in which you pass your cables and can hide the tanks, bilge, batteries, etc... under) or it was made for another boat and put into this one as a temporary storage solution but then sold the other boat and never put the tank in it... (dimensions fits in between the 2 longitudinal Z-brackets though... which would be a coincidence I guess!)

Condensation could be a thing indeed, but as I mentioned, I wouldn't make my flooring go tight to the sides, so there would still be fresh air going in/out of there. Don't know if it would be enough though ? As I just replied to the other comment; I've never redid foam or hulls before, so I wouldn't be able to tell.

You're right about COG, but would it realistically change much? I mean, it's a 18.5ft hull with pretty high sidewalls, something like 30" I believe (has something like 6-8 inches above the "long shaft" cutout in the transom...)

 

[MrGiggles]

(I don't know if it has a name, the aluminum plate that is weirdly shaped in which you pass your cables and can hide the tanks, bilge, batteries, etc... under)

Splashwell. On many setups with an in-floor tank, the rear section runs underneath the splashwell, and that's where the fill, return, and pickup fittings will go. The filler neck often runs up through the splashwell, most pumps will reach there easily and you don't need to climb into the boat.

You can buy a screw in style fuel pickup assembly and put it pretty much wherever you want in that tank. The filler neck can be a little trickier, but still doable.

 

[thill]

The ACM is stiff, but what happens when it gets in the sun on a hot summer day? That would be my concern. Maybe buy a sheet and see how it is when it's 95 degrees. Please pass it on if it stays stiff and works well OR if it doesn't. I've seen that stuff buckled before, but not sure if it's the same product you refer to.

Me, I typically use 5/8" BC Ext. plywood soaked in Thompson's Wood Preserver. Have been using it for many years, and it just works. Relatively light and very strong. It spans much farther than 1/2" and I've yet to see it rot or even start to get springy or soft. I did my Princecraft 10 years ago or so, and it's as rock-solid as the day I did it. And it's only $40 a sheet and well-proven.

Still, that ACM is an interesting concept. Please let us know what you find out.

 

[PunkR0ckz]

The ACM is stiff, but what happens when it gets in the sun on a hot summer day? That would be my concern. Maybe buy a sheet and see how it is when it's 95 degrees. Please pass it on if it stays stiff and works well OR if it doesn't. I've seen that stuff buckled before, but not sure if it's the same product you refer to.

Me, I typically use 5/8" BC Ext. plywood soaked in Thompson's Wood Preserver. Have been using it for many years, and it just works. Relatively light and very strong. It spans much farther than 1/2" and I've yet to see it rot or even start to get springy or soft. I did my Princecraft 10 years ago or so, and it's as rock-solid as the day I did it. And it's only $40 a sheet and well-proven.

Still, that ACM is an interesting concept. Please let us know what you find out.

The issue is, I am from Canada, close to Montreal, we rarely get 95F, it's usually under 90F, and I don't go fishing above 70C cause I'm a cold blooded MF. I would rather go when it's 40F then 90F lol

As far as the ACM goes, it's "aluminum composite material", the aluminum sheets they use for vertical outdoor walls in modern builds. I passed on the frames I showed in the original post because I realized it would be a hassle to modify it to fit my boat after seeing the dimensions it had (would need to cut too many pieces and whatnot). I'll surely post updates as I go on, but right now the build isn't my priority I gotta deal with house stuff that's much more important.

I might also start a brand new thread where I will post updates and whatnot instead of scattering them all over the place. We'll see how I feel at that time. Can't wait to empty my garage to be able to work on my ATV and the boat.