- Location
- Red Bluff CA
Also, a superjet that isn't waterlogged will bob the tray almost entirely out of water. I used to have a Pic of one in shasta.
How important is foam density?
- Thread starter Roseand
- Start date
Consider the skis specific gravity, that is what it weighs underwater. An entire ski will be around 3. That will require a little under 2 cubic feet of foam to make a hull float. Density of the foam comes into play when its used structurally. For floatation lighter is better.
Last edited:
This is an interesting point that I had not considered. Googling around briefly, I see that the specific gravity for fiberglass is roughly in the neighborhood of about 2. The resin is just over one and the fiber is more like three so it depends a bit on the proportions of resin and fiber but you end up around 2-ish. So there is a non-trivial amount of flotation from the fiberglass itself, roughly half of it's own weight. If you have a hull with ~100lbs of fiberglass, which is probably typical of a fiberglass hull, you have 50 lbs of buoyancy just from that.
Aluminum just under 3, steel is about 8, rubber about 1.
So overall 3, seems plausible.
As I remember from my days as a lab tech, our glass panels were just under 2.5 and carbon was just under 1.8.
Pic is of my circus build to show that there is some room for foam. There is two pieces of carbon with a 1” wide piece on top that yet to be epoxied into it. l think structurally it’s solid @Jr. And knowing a superfreak, it is gonna corrode parts after a few years and it would be dick to have to clean all that foam out.
Attachments
- Location
- Red Bluff CA
Is it really that hard to figure out how something floats? For a strictly water sport, people seem to be oblivious. Maybe none of you ever swam? All sorts of trickery and calculation. When you can just stick something in the water. And feel how buoyant it is. Can make rocket surgery out of anything I guess.
- Location
- Red Bluff CA
Like I said. Almost the entire tray
You know this a forum where we discuss things and share knowledge right? lsn’t that we are doing here.
- Location
- Red Bluff CA
Discussing a floating jet ski? What is there to discuss? Properly foamed skis float better and take damage better than un foamed skis. That cannot be discussed as it's a fact.
Trying to generalize the floatation of a ski, on the internet. Isnt going to help anyone when their ski sinks. A better idea for ski loss prevention is tactics to avoid sinking, or prevent it going under.
This thread is titled. How important is foam density. It's pretty obvious that 1 or 100 pound foam displaces the same water for given size/volume. And 100 pound foam is going to be harder than 1 pound foam. So if you want your ski to float. Foam is very important. If you want the tray to hold its shape well against impacts. Density is important.
Takeaway from this; your jet ski should be foamed and anyone who says otherwise is a pro level rider chasing 2 or 3 degrees of rotation. Or a gimmick chaser who has to have the most tricked out ski.
SXIPro
JM781 Big Bore
- Location
- Here on the 'X' mostly
Just gonna build my next hull out of foam. Two birds, one stone.
I want to add more speculation and unnecessarily complex theoretical calculations so bad right now. What if we factor in water temperature, salinity, and atmosphere pressure? Salt water is more dense than fresh water isn't it?
What if you had a bag of salt on your ski, when it sinks the salt dissolves in the water increasing salinity and the density of the water thus increasing the buoyancy of the flotation foam.
What if you had a bag of salt on your ski, when it sinks the salt dissolves in the water increasing salinity and the density of the water thus increasing the buoyancy of the flotation foam.
At the risk of getting yelled at because I notice you always seem so annoyed by everyone in your posts, but we are discussing HOW to properly foam a ski. Believe it or not there are ways to do this scientifically beyond the scope of redneck garage. I don't think anyone is debating whether a ski with foam floats better, this is obvious. You can certainly stick something in water to see how it floats, like you recommended, but that is after the tray is all sealed up and the build is finished. This is a little bit backwards as the idea here is to making sure you get it right prior to testing...
- Location
- Texas
Foam Density matters IF you need to add Structural Strength to the Hull.
Otherwise, the same Volume (say one cubic feet) of 2 lb Foam will displace the same amount of Water as 6 lb Foam.
For every Cubic Feet of Water displaced, you gain around 62 lbs of Buoyancy.
But the 8 lb Foam weighs a little more, so that will take away some Bouyancy.
Otherwise, the same Volume (say one cubic feet) of 2 lb Foam will displace the same amount of Water as 6 lb Foam.
For every Cubic Feet of Water displaced, you gain around 62 lbs of Buoyancy.
But the 8 lb Foam weighs a little more, so that will take away some Bouyancy.
WFO Speedracer
A lifetime ban is like a lifetime warranty !
- Location
- Alabama
Redneck has always worked just fine for me, ya'll gourd head.
He does seem kind of annoyed with these petty questions
SXIPro
JM781 Big Bore
- Location
- Here on the 'X' mostly
The King grows tired of the nonsensical inquiries of the simple minded serfs and peasants. OFF WITH THEIR HEADS!!!
- Location
- Ontario, Canada
The" ignore" (or should be called block) feature is a beautiful thing, ask me how I know
- Location
- Downers Grove
I can tell you that a circus freak with a 2 gallon tank in the front and no foam, but a fairly well sealed tray will float just below the surface as long as you hold the scupper ball closed as it goes under. No idea how much air that was actually holding in by the end as it was probably 15 minutes before I got pulled out by a boat. A Gen 1.5 full length freak with no foam, a fully sealed tray air chamber, and a stock superjet tank will float itself with a mostly full tank. A RIP will give you about 35 seconds between when you think this ski feels heavy and when it is 12' under as you are slowly releasing the safety rope that you tied onto the front before the test ride. I swear a flat rock will sink slower.