Approximate dry weight of a 16 foot super sport?

[ShoestringMariner]

Hey fellas, I’m trying to figure out the dry weight of my boat as it would’ve come from the factory. I found something on the web that unofficially states an18 foot is roughly 850 pounds. I would have to assume that this is without a motor, battery etc. ( basically helm, flooring, steering, windshields seats etc.)


What I’m trying to determine is whether I can get enough flotation foam into mine that will be enough to prevent worst case scenario of total loss. (Sinking to bottom) The foam that is in mine is totally waterlogged and garbage. I’m replacing with dense styrofoam SM. I’ve done under the floors and 12 inches up the side of the hall for the first 2 feet of the boat so far and I’ve used one 2“ x 24“ x 96“ board. From what I can find each board should support around 160 pounds of buoyancy give or take a few pounds.

I’m doubtful I can stuff this much Styrofoam into my boat. To support my boat, motor, starting battery, trolling battery, trolling motor, anchor etc, I’ll need somewhere in the neighbourhood of 9 or 10 of these boards.

have any of you restore guys managed to cram that much Styrofoam in your 16’ boats?

do you consider the plywood to be neutral weight since Wood typically floats on its own?

 

[Scott Danforth]

look it up yourself

http://boatspecs.iboats.com/

use pour in foam, styrofoam is the wrong material, you want closed cell poly foam

the factory already did the calculations for you, simply replace with same volume of 2# foam

 

[Michigan Lakes]

Just about everyone on here uses closed-cell xps board for their foam replacement. This is quite possibly what you are already using. I would've just called it "styrofoam" as well prior to iboat research.

https://www.homedepot.com/p/Owens-C...ared-Edge-Insulation-Sheathing-52DD/202085962

Pour-in will work but you'll need to take measures to ensure any water below the deck can still drain properly.

 

[bchaney]

Check the brochures in the sticky. Nothing for your 1975 and the 74 and 76 are unclear but for 77 the dry weight of a 16SS was 660lbs.

As for the foam discussion, expanded polystyrene (EPS /Styrofoam) is closed cell but the concern is that it's somewhat brittle. The blocks may break apart into little beads if it's in a place where it bounces around while underway. Most people seem to use use expanded polystyrene (XPS) because it's more durable. Personally I would have no problem putting EPS in my boat if it is well secured and not in a place that may put force on the blocks. Others will probably disagree with me on this.

https://www.flickr.com/photos/starcr...57622763946729

 

[MTboatguy]

My 73 is listed at 630 and I weighed it when I got it and that is pretty darn close, that was with 2 seats and the engine which is a 73 Evinrude 50 hp. I would imagine, depending on you have it equipped it will be close.

 

[ShoestringMariner]

Thanks guys, I figured 650ish. And that looks like with the motor too? seems very light.

Im using the dense blue closed cell styro. It’s called Styro SM here. Does not absorb water or crumble. Very rigid and tough. Likely same as the XPS mentioned.
Scott Danforth , At first I couldn’t imagine the factory foam being even remotely close enough, even if not waterlogged, but if these boats are only 650ish lbs WITH motor than maybe it’s close

 

[ShoestringMariner]

This is basically what I’d like to achieve, or close. Not that I’d want to test it

https://m.youtube.com/watch?v=nub_Cm8PoqU

 

[roscoe]

This is basically what I’d like to achieve, or close. Not that I’d want to test it

https://m.youtube.com/watch?v=nub_Cm8PoqU

Yeah, always had a problem with that lund commercial.

Looks like all that foam was a cheaper and easier solution to making the hull feel more rigid.


Remember, the goal is to keep the boat from sinking to the bottom, and give the people something to hold on to.

mine sinks stern first, until the transom is submerged.
Then the water start speaking out and pretty much levels the boat.

Yes, 6.5" of rain fell in about 2 hours and filled the boat, then the waves came over the transom.

 

[DLNorth]

I suspect that the weights listed are "dry" w/o motor, as the manufacturer doesn't know what motor will be put on.

IIRC our 70/71 SS16 is listed at 570, a bit lighter then slightly newer versions, maybe due to the plastic windshield, that was changed to Safety glass a year or 2 newer, then it is listed at 650.

Dan
ps, a V4 OMC (85hp) is close to 300 lbs, a 4 cyl Merc 850, about 265, not sure what a 3 cyl OMC is but likely in the 230-240 range.

Thanks guys, I figured 650ish. And that looks like with the motor too?
.................but if these boats are only 650ish lbs WITH motor than maybe it’s close

 

[ShoestringMariner]

I suspect that the weights listed are "dry" w/o motor, as the manufacturer doesn't know what motor will be put on.

IIRC our 70/71 SS16 is listed at 570, a bit lighter then slightly newer versions, maybe due to the plastic windshield, that was changed to Safety glass a year or 2 newer, then it is listed at 650.

Dan
ps, a V4 OMC (85hp) is close to 300 lbs, a 4 cyl Merc 850, about 265, not sure what a 3 cyl OMC is but likely in the 230-240 range.

See, and I was having trouble with that weight all along. What you’re saying makes much more sense. I initial thoughts were that this boat would’ve been 1000 pounds dry weight as equipped meaning equipped with a motor. I’ve got a 65 merc on it now. I just added a CMC tilt. I believe you are right about engine weights. The 70 I want to put in it Is about 230 some odd pounds Without tilt. Factory tilt brings it up to almost 300 pounds.

add bow mounted trolling motor and battery.... eight horse kicker off the back...
I need a LOT more flotation foam than what the factory originally provided. Like around 20 to 22 ft.³ of foam

 

[DLNorth]

In your calculation, how are you determining the volume of the boat when submerged?

and from the web,

"MAST trials show that boats that have underfloor buoyancy were not likely to remain upright but would float either upside down or bow up depending on the weight of the outboard and the buoyancy fitted in the stern of the boat.

Flotation material added at the sides, as far aft and as high as possible (up under the gunwales) will under normal conditions, make the boat float level. Even if the boat is swamped, it will stay upright and sit lower in the water, even to where the deck is level with the surface of the sea or surrounding water. If the occupants are tipped out they can get back into the upright boat more easily."

 

[ShoestringMariner]

In your calculation, how are you determining the volume of the boat when submerged?

and from the web,

"MAST trials show that boats that have underfloor buoyancy were not likely to remain upright but would float either upside down or bow up depending on the weight of the outboard and the buoyancy fitted in the stern of the boat.

Flotation material added at the sides, as far aft and as high as possible (up under the gunwales) will under normal conditions, make the boat float level. Even if the boat is swamped, it will stay upright and sit lower in the water, even to where the deck is level with the surface of the sea or surrounding water. If the occupants are tipped out they can get back into the upright boat more easily."

Excellent, thanks for that. I’m not sure I understand your question about submerged volume. I’ve been pondering dead weight of the boat versus buoyancy materials added. If a boat was totally swamped and completely filled with water, would it not still float if the buoyancy of materials exceed the weight of the boat and gear?

In such an instance, I figured the stern would be the hardest to support. Especially with a kicker on back. I also found what you provided interesting in that a swamped boat with only under floor floatation will tend to go bow up or possibly upside down. I am planning on putting foam 12 inches up from the floor level for the full length of the boat and into the bow. I’ll also fill underneath the bow and gunnels. I may even clad the transom and underside of the splash well if there’s enough room for fuel cans and battery access.

My primary concern is to keep this boat afloat enough to a) have something to cling to should we be stranded and completely swamped, b) limp back to shore safety should be tear a hole in the hull, c) prevent a total loss of boat and equipment. I don’t ever see using this boat in big water where huge waves and swells could capsize us but I’d like to be a plan for everything and anything

 

[MTboatguy]

I see I goofed yesterday, I said was 630 with my motor and 2 seats and it should have been WITHOUT, sorry about that, my 50 hp rude weighs like 193 and the seats are about 20 pounds each.

 

[DLNorth]

To determine the buoyancy of a SUBMERGED boat, you need to know the volume of water displaced, which is the volume of the boat, motor, seats, tanks and all other gear that is submerged and displacing water. Not an easy thing to determine or calculate without a cad model or a test tank that the boat can be sunk in and the volume measured.

The easiest thing to do might be to go look at a relatively new SS16 and see where they put the additional flotation material to achieve the CG level float requirement. The few I've seen, IIRC, just had large blocks on either side the the SW under the gunwales. I would SWAG it at about 2.0 ft^3 each side.


" If a boat was totally swamped and completely filled with water, would it not still float if the buoyancy of materials exceed the weight of the boat and gear? "

 

[ShoestringMariner]

To determine the buoyancy of a SUBMERGED boat, you need to know the volume of water displaced, which is the volume of the boat, motor, seats, tanks and all other gear that is submerged and displacing water. Not an easy thing to determine or calculate without a cad model or a test tank that the boat can be sunk in and the volume measured.

The easiest thing to do might be to go look at a relatively new SS16 and see where they put the additional flotation material to achieve the CG level float requirement. The few I've seen, IIRC, just had large blocks on either side the the SW under the gunwales. I would SWAG it at about 2.0 ft^3 each side.


" If a boat was totally swamped and completely filled with water, would it not still float if the buoyancy of materials exceed the weight of the boat and gear? "

SWAG = splash well and gunnels??

 

[bchaney]

I think it means Scientific Wild *** Guess.

You may already know this but just because your boat weighs 1000lbs out of the water doesn't mean that you need enough foam to float 1000lbs. When the boat is submerged it will weigh much less than 1000lbs. You are getting some buoyancy force from the water just due to the fact that your boat is displacing it. Buoyancy force = weight of fluid displaced by object. If you can approximate the volume of your boat you can multiply that by the density of water to get the buoyancy force and subtract that from your 1000lbs to come up with a minimum amount of flotation foam needed.

 

[DLNorth]

Close
Silly Wild Axx Guess

And B, you said it better than I did, that's what I was trying to get across above.

 

[ShoestringMariner]

Lol, ok, I get that you’re saying, but let’s say the boat is completely swamped to the point that the transom is under water and water has flowed right in. At that point, the boat is no longer displacing anything. Wouldn't dead or dry weight vs buoyancy not be directly correlated?
Like pushing a 10lb container into a pail of water...once it comes pouring over the sides, all is lost and it sinks to the bottom. Attach 10.1 lbs worth of floatation medium, and it should float, albeit barely. No?

 

[bchaney]

You're right that in a swamped state it's displacing less than when it's afloat, but it's still displacing water. All of the materials in your boat have volume - aluminum sheets, plywood, seats, motor, etc. All of those things weigh less when they're in water than when they're in air. Ever notice that your anchor feels lighter when you're pulling it up thru the water than those last few feet between the water surface and into the boat? Same thing.

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[ShoestringMariner]

You're right that in a swamped state it's displacing less than when it's afloat, but it's still displacing water. All of the materials in your boat have volume - aluminum sheets, plywood, seats, motor, etc. All of those things weigh less when they're in water than when they're in air. Ever notice that your anchor feels lighter when you're pulling it up thru the water than those last few feet between the water surface and into the boat? Same thing.

​​​

Well I'll be darned, you are absolutely right! I am amazed at this. I should have studied physics

I found this on the web; "Whatever the density of something is in air, it's one gram per cubic centimeter less inwater because the water supports that weight. Aluminum has a density of 2.7 gm/cc in air, and 1.7 in water"

VERY interesting stuff, thanks for pointing it out