Experience, guidance, considerations on raising main deck / floor of aluminum boat

[PikeHunter431]

I didn’t see a lot on this topic in my (potentially feeble) search attempts. So I thought this might be a good discussion beyond my particular restoration.

In my particular situation, I am restoring/redesigning an 18’ Starcraft SS. (there is a separate discussion for just that). I'm looking at things like underdeck gas tanks, putting in additional underdeck storage, adding a rear deck, putting in a 24 volt (thus 2 marine batteries) trolling motor system and a 150 qt livewell. At the same time I would like to beef up the floatation and be able to get the boat to plane with moderate power Tt would seem one option would be to raise the floor/main deck above the stringers, thus providing new room for foam for the flotation.

A couple items I have seen about this:

1. The front consoles are designed for the current level of the floors, so that would need to be dealt with.
2. There are probably some structural implications; I am thinking of where the floor meets the sides of the hull.
3. You are changing the center of gravity. So at some point this may be impactful. Not sure where this would happen. 1”, I doubt it, 12” I imagine so.
4. You need to provide support under the floor, particularly to the stringers. (what approaches have been tried and to what success/failure).

The issues reach beyond an 18’ SS and beyond Startcraft boats to other tinnys. So what say ye tinners?

 

[Bondo]

Ayuh,.... My thought is, much like the guys that wanta turn a 12' tinny into a flat decked bassboat,....

Yer headed down the road of puttin' 10lb.s of poo, in a 5 lb. sack,.....

The hull is still limited to it's original weight limit,.....

Just yer livewell, 'n batteries is the equivalent of up to 2 people,....

 

[Ned L]

Yep,... You are heading in two different directions at the same time.
You say "At the same time I would like to beef up the floatation and be able to get the boat to plane with moderate power". This means minimum weight, and do whatever you can to reduce weight and keep it down. Then you list all the changes you want to make, which will be a LOT of weight. The two don't go together.
Oh, and just to make sure we are all clear,... foam flotation is nothing more than extra weight in the boat, it does not help performance at all, (until the boat fills with water and you need it).

 

[PikeHunter431]

I don't think we are on the same page here. I understand the trade-off of weight to performance. The topic is also bigger than just my situation.

As for my situation, let's assume the following: I will be heading toward the rated weight of the hull. There is stuff / items that may be stowable underdeck. This may mean raising the deck to still have enough flotation (and yes flotation does add weight) such that the boat level floats if swamped. Where I fish, if the boat sinks, it could be many hundreds of feet deep and non retrievable. At the same time, I prefer to have things in their places and out of the way. On the performance, I was only looking to get the boat to plane, which is sometimes a "where the weight is distributed" issue as much as a power issue. Doing things like moving a rear above deck gas tank to forward under deck, I believe, would assist planing. Please let me know if this is incorrect. I am not looking to have a "performance" boat per se, but only being able to get up on plane. In the future, I may also be beefing up the horsepower. however, the deck design is likely to be done before that.

 

[Ned L]

To an extent you are correct about shifting weight forward, however moving it too far forward can create real squirrely performance at higher speeds. There can sometimes be a fine balance here.

 

[Woodonglass]

Is there a reason you felt this question was not appropriate to be posted in your already started boat thread?? Having multiple threads started about the same boat can soon become very confusing to the members.

 

[PikeHunter431]

Hi WOG. When I searched on this, I didn't find much on it (except for fiberglass boats). Perhaps my searching was not thorough enough and there is alot out there. I thought the discussion, beyond my boat, may be of use for others. I tried to frame it as a general type question. I used my particulars as an example for why someone may want to do such a thing and the few points on the subject I did find. The invitation was to also generate a pooling of knowledge, some of which may not be applicable to my particular restoration. I thought that might have some value and be easier to find for others with questions on this subject.

 

[64osby]

Pike, If you want to add additional foam - add it under the gunwales, bow cap and splash well. All of those would provide enough flotation to float your hull and not have the necessity of raising the floor / deck.

Weight distribution of batteries and a live well is a matter of how you use your boat and how it is laid out. Location of batteries can be front mid or back, it's just a matter of wire size and length. Livewell location is again a matter of how you choose to layout the boat.

I would would not raise the floor / deck do to structural issues. Raising it could or would create hard spots or wear points on points of the hull that were not designed to have "hard" spots.

My .05

 

[Bondo]

This may mean raising the deck to still have enough flotation (and yes flotation does add weight) such that the boat level floats if swamped. Where I fish, if the boat sinks, it could be many hundreds of feet deep and non retrievable.

Ok,... I think yer puttin' to biga empiricism on the floation foam,....

Our boats usually don't sink like a rock if capsized, it ain't gonna sink like the Titanic in the movies,....
Much of what's in our boats floats by itself, which adds buoyancy to the hull,...
Wood decks, coolers, Pfds in the lockers, toilet paper in the plastic bag, gas tanks,.... it all adds up,...

No way I'd loose valuable space, much less raise the CG, just to add more foam,.....
Personally, I've Always been against foam, it rots out our hulls,....

If ya feel it's Necessary, go for it, but I wouldn't add more than there was,......

 

[GA_Boater]

Yep - This should have been the original thread, but heck, this is theoretical because it's a bad idea.

How high a raise? What free board will the result have?

Do you know the deck is one, if not the most important structural element in a Starcraft? How will a deck be tied into the primary existing deck support structure - the ribs?

A raised fore or aft deck is one thing, but raising the entire deck is not wise, even to add more flotation.

 

[oldsub86]

I find the idea interesting. I have wondered if I could do that to my old Lund. My reason was to hopefully make it self draining. Then if it sat at the dock and got rainwater in it, I would not need to worry about the bilge pump getting plugged up etc. If I could raise the floor a bit, it would drain out through some holes in the transom. I would need to seal the edges of the deck in some manner and put a curb around the engine (I/O) but that should be doable. My old boat is deep enough that I doubt I would feel like I was going to fall out if I raised the floor 6 inches.
I think it can be done and I hope you do it and post lots of photos of the job and then let us know if it worked out as well as you hoped it would.

 

[PikeHunter431]

Hi oldsub86, I thought the idea was interesting as well. I sincerely doubt I would raise the deck in my case without a better understanding of what the issues were, how they have been dealt with and see some way to do it that would meet my needs and situation as well as be safe, manageable, etc. I have to believe others have wondered about this and hence why I started the thread. Perhaps it is a bad idea for a host of reasons such as a,b,c, and d, whatever. If so, let's get them out there so we understand why.

 

[PikeHunter431]

Hi 64osby, thanks for the input. I agree with the other options you laid out. I was pretty sure there would be structural issues. I just had/have no clue as to what the actual structural issues are, what, if anything, people have done and their experience there.

 

[PikeHunter431]

Hi GA_Boater, Like above, I understand the floor/deck is very important structurally. On your other questions, I don't have any particular amount. Is there a difference in the issues depending on the amount of rise? I believe I have seen that a couple folks raised their floors slightly to accommodate under deck gas tanks. I don't think I saw what the structural issues were, how they dealt with them and any insights afterwards. My guess is they were raising the deck 1 - 3 inches. I don't know. That is part of what I was putting out to the fleet for us to find out.

I haven't done any flotation calculations yet, partly because I haven't designed the modifications yet. I did read some of the flotation threads and often saw people come out with they basically had just about the right amount when they were done. That led me down the thought path of if someone was going to use some of the space where they had their foam and/or add additional weight it, then there would need to be some additional space somewhere to put the foam. The other peripheral thought I had was around the need to have good drainage under the deck. That is either having the foam up off the hull, so to speak and / or channels in it. Either way, it is volume of space issue and can that space be expanded. I am pretty sure it is a bad idea not to have those spaces for drainage. Maybe the answer is there is no good way to raise a deck, maintain structural integrity, and not damage the boat. In that case one should look at the space under the deck as fixed, period. I dunno.

 

[PikeHunter431]

Personally, I've Always been against foam, it rots out our hulls,....

If ya feel it's Necessary, go for it, but I wouldn't add more than there was,......

Hi Bondo, I'm confused. Are you suggesting taking the foam out and not putting anything back in or to use some alternative to foam?. The tinny restores I looked through all seemed to put some type of foam in. The only variations I saw were in what kind of foam they put in. I am a neophyte here. I appreciate any insights you have on this.

 

[Bondo]

Ayuh,..... There's No foam in most boats over 25' or so,...... Ya know, Bigger boats,....

Not sayin' you should pull all the foam, 'n put nothin' back in,.....

Poured 2 pt foam is a hull killer,....
Foam strips, pool noodles, etc ain't so bad, just a waste of space,.....

To each his own,.... Only little hulls are required to have it, per CG, 'n only by Oem's,....

 

[Tnstratofam]

I haven't weighed in on your other thread, but have been following along. This is an interesting thought that probably pops up more than is discussed here on the forum. I think lots of people " myself included " purchase the boat or restoration project their budget allows with the thoughts of having a do all boat. Some people want a fishing boat that has the stability of a tri hull, the ride of a deep vee hull, with the casting deck of a bass boat. Others want a pleasure boat they can also fish out of.

While their are probably some examples out there of multi purpose boats ( Fish and Ski's come to mind ), most boats are designed to be one thing and do that one thing well. Trying to change the layout from the original design can be tricky, but it can be done.

For example we have a Starcraft SS 160 bow rider that was originally designed as a pleasure boat. We have it set up for fishing now. I have a removable casting deck incorperated into the bow seating area and store our tackle boxes along with some miscellaneous items in the under seat storage. We usually have a cooler with sandwiches and drinks which can be moved forward or aft or port or starboard for weight distribution. I have a trolling motor and battery in the bow, with my start battery and two 6 gallon gas tanks under the splashwell. I have retained my bow seating with two swivel style captains chairs at the two consoles. The rear deck is open for casting although sometimes my step son will sit their when we are cruising on cold days.

That layout works good for keeping the boat stable both at rest and underway, although moving gear and or people around to keep us on an even keel is a regular process depending on who and how many come along. I had thought about a belly fuel tank as well as a livewell at one time, but there isn't really enough room without moving them forward of what I think is the center of the boat. This could create a situation of plowing while underway, and having the two portable fuel tanks allows me to balance the boat better as I use fuel up when I am by myself. A live well may still be an option as it could be placed where the ski locker once was. Raising the deck could allow for the fuel tank or livewell to be stored underneath, but it would also change the center of gravity making the boat more unstable in the water. My casting deck is about a foot higher than the main deck, and it can be a little bit of a balancing act when I'm fishing and ther is a sudden side to side movement.

Not to mention raising the deck would require adding more structure for support which is added weight that affects performance as well as safety.

Our boat is the 16 foot little sister to yours in a sense so I would think it would be similar. I would recommend checking out budski's restoration projects as well as some of the other Starcraft restoration threads to see how others have modified their tin boats to fit their needs. Their are lots of ideas floating around out there and picking the one that works best, or the ones that fit your needs are the good thing about others going through the process before you. It's also why posting not only our success at modifications , but also our failures is what makes these forums work.