SJ build - removing bulkhead entirely?

[WFO Speedracer]

Just kidding its a J/K........ :biggrin: I am in a funny mood today. :biggrin:

Mark44

It wasn't directed directly at you well not directly that is lol:Eyecrazy:

 

[Glory_Freestyle]

The only torque the bulkhead sees is what is created by the drag of the intermediate bearing/seals which is fairly minimal.

True. I guess the only time where torque would be a problem there is if the bearings lock-up or some other pump related problem.

What about a more rounded cut-out? I always hate leaving holes square because of the minute chance of cracking at the corners. See Blue in pic.

Of course, the bulkhead is probably too think to worry about that, but just throwing it out there.

 

[Mark44]

How about just taking a 2" hole saw and cutting out a hole on each side of the bearing mount area about a 1/4" off the deck less destruction the the structural integrity and will do the same thing.

Mark44

 

[Dustin Mustangs]

I just thought I'd weigh in on this buoyancy conundrum due to the fact that I just went over this topic while studying for the pe this morning.

To determine buoyancy you need to know three things; mass of the object, volume of the object and density of the fluid(s) you are putting it in. Mass and density are pretty easy to get (although do realize that fresh water is 62.4 #/cf and salt water is more than 64 #/cf). Now the volume for a ski would be pretty much impossible to calculate accurately even when floating, let alone when sunk. The only way to get a good number for this would be empirically which I am sure is how the original engineers did it. Now unless someone has a graduated container sitting around big enough to fit a ski in (and the cojones to sink one in it) that option is out.

Long story short, the amount of foam needed can't realistically be accurately calculated. A safe shortcut would be to measure/calculate the volume of the foam you are removing (and not putting back) and add that same amount (or more) somewhere else in the ski. This will work assuming that it floated originally and that the foam you use is the same (or a lighter) density as the original foam.


opworm:



edit: I would also strongly agree with what glory said above about the shape of the holes.

 

[snowxr]

Here's what your bulkhead could look like. j/k

 

[smoofers]

Honestly, taking all of that foam out would not really have a positive outcome in my opinion... The amount of foam removed would equal what, 5-10lbs max? In effect you are just making your ski that much more prone to sinking. As I am an engineer (not as far along as Dustin, good luck on the PE!) and am cursed to think like one, I think most people don't realize that the foam does not make the ski more buoyant, it just makes the fillable volume inside the ski smaller. A hull full of foam will float just as well as an empty hull, only difference is when you submerge the hull full of foam, the foam is displacing a large amount of volume for its given mass. Seeing as how all jetski hulls are anything but watertight when you submerge them, if you submerge a ski with no foam, less water is displaced for the mass of the whole, and you have a ski that will sink to the bottom like a rock. A good comparison would be to imagine (or try it yourself) an empty beer can. If you were to fill the can half full with foam, and then try and sink it, it will probably still float with a large portion of it above water. Now try the same thing with an empty beer can and no foam.....

Comparing my HX to the configuration of the SJ, I wish I could fill up the empty space under my footwells with foam, but then it would be a huge pain to remove exhaust hoses etc. In my opinion foam is a good thing, and very cheap insurance. I can understand if your foam is waterlogged from years of riding, but you are starting fresh. Just put some nice new foam in there, and you are good to go for ten more years. If you are hell bent on pulling some foam out, I still think the best compromise would be two lengths of 2" PVC pipe (just like a scupper setup...). It will give you your desired result and keep some structural integrity.

Just my 2 cents

 

[SuperJETT]

I think people are missing the point, it's not that I'm taking foam out because I plan on foaming the nose to replace most of the missing foam, it's that the area under the tray is where all the water leaks come from resulting in waterlogged foam. So, I want to keep that area open and even serviceable if need be.

The upper deck gunwales will be foamed and glassed over prior to assembly, so it won't leak. The nose will be done the same way so it won't leak. My handle pole has foam and I use 25mm underpad which adds floation as well.

BTW, I have plenty of experience with buoyancy, etc. I've done a few rough calculations based on hull side/thickness/weight and feel ok about things at this point.

 

[JonnyB]

I can understand if your foam is waterlogged from years of riding, but you are starting fresh. Just put some nice new foam in there, and you are good to go for ten more years.

A LOT of people have found water in foam after only one season of defoaming/refoaming

 

[WFO Speedracer]

Honestly, taking all of that foam out would not really have a positive outcome in my opinion... The amount of foam removed would equal what, 5-10lbs max? In effect you are just making your ski that much more prone to sinking. As I am an engineer (not as far along as Dustin, good luck on the PE!) and am cursed to think like one, I think most people don't realize that the foam does not make the ski more buoyant, it just makes the fillable volume inside the ski smaller. A hull full of foam will float just as well as an empty hull, only difference is when you submerge the hull full of foam, the foam is displacing a large amount of volume for its given mass. Seeing as how all jetski hulls are anything but watertight when you submerge them, if you submerge a ski with no foam, less water is displaced for the mass of the whole, and you have a ski that will sink to the bottom like a rock. A good comparison would be to imagine (or try it yourself) an empty beer can. If you were to fill the can half full with foam, and then try and sink it, it will probably still float with a large portion of it above water. Now try the same thing with an empty beer can and no foam.....

Comparing my HX to the configuration of the SJ, I wish I could fill up the empty space under my footwells with foam, but then it would be a huge pain to remove exhaust hoses etc. In my opinion foam is a good thing, and very cheap insurance. I can understand if your foam is waterlogged from years of riding, but you are starting fresh. Just put some nice new foam in there, and you are good to go for ten more years. If you are hell bent on pulling some foam out, I still think the best compromise would be two lengths of 2" PVC pipe (just like a scupper setup...). It will give you your desired result and keep some structural integrity.

Just my 2 cents

I tried explaining this earlier,it went right over some peoples heads,whatever its no biggie to me as my boat won't be the one sinking.:thinkerg:

 

[Ericfox]

pingpong balls dude...

 

[snowxr]

I think 24/7 has the ping pong ball market cornered

 

[snowxr]

I think people are missing the point, it's not that I'm taking foam out because I plan on foaming the nose to replace most of the missing foam, it's that the area under the tray is where all the water leaks come from resulting in waterlogged foam. So, I want to keep that area open and even serviceable if need be.

The upper deck gunwales will be foamed and glassed over prior to assembly, so it won't leak. The nose will be done the same way so it won't leak. My handle pole has foam and I use 25mm underpad which adds floation as well.

I think you're on the right track. I've made some 2Lb. nose foam replicas to glass into my ski's nose. Gotta figure nose foam + gulwhale foam + lighter topdeck = :brap: solid ski.

 

[Speedfreak]

I posted this quite a while back and I got a bunch on negative responses.

I really don't care about sinking. I have TONS of insurance and in my life have never sank a ski. And if I do that is where the insurance thing comes to play.

I would do it in a heart beat. It is the smartest thing you can do. never have a foam problem again. I would also mount dual scuppers in the back. What are the chances that a ski quits running and the battery is dead or the bilge pumps lock up all at the same time. I know that it can happen but what are the chances.

Here is my old thread http://www.x-h2o.com/threads/38516

 

[SuperJETT]

I posted this quite a while back and I got a bunch on negative responses.

I really don't care about sinking. I have TONS of insurance and in my life have never sank a ski. And if I do that is where the insurance thing comes to play.

I would do it in a heart beat. It is the smartest thing you can do. never have a foam problem again. I would also mount dual scuppers in the back. What are the chances that a ski quits running and the battery is dead or the bilge pumps lock up all at the same time. I know that it can happen but what are the chances.

Here is my old thread http://www.x-h2o.com/threads/38516

I didn't see or don't remember your old thread, that is interesting.

I honestly can't recall that I've ever completely sunk a ski before, though I've helped bring in others. I know it can happen though.

 

[Matt_E]

I would do it in a heart beat. It is the smartest thing you can do. never have a foam problem again.

This is what prompted me to do something different about my hull.
I went with water proof polystyrene foam and drainplugs.
Never waterlogged foam again.

 

[cambo au]

i like it and would do it after reading the entire thread i was thinking i will take everyones negs and say what if you glass just the middle between the bulkhead and front of the pump and foam it as well as the nose and the top gunwhale section
that way you dont have to worry about the torque on the bulkhead ,the tray has support all the way to the front there is also a little more foam if your worried about that i really like the idea i just think the underside of the tray need support a least with my 220lb ass landing on it in the surf

 

[snowxr]

I totally aggree that enclosing the area in front of the pump is the right way to go if foaming the upper gunwhales.

 

[Idok]

I think people are missing the point, it's not that I'm taking foam out because I plan on foaming the nose to replace most of the missing foam, it's that the area under the tray is where all the water leaks come from resulting in waterlogged foam. So, I want to keep that area open and even serviceable if need be.

The upper deck gunwales will be foamed and glassed over prior to assembly, so it won't leak. The nose will be done the same way so it won't leak. My handle pole has foam and I use 25mm underpad which adds floation as well.

BTW, I have plenty of experience with buoyancy, etc. I've done a few rough calculations based on hull side/thickness/weight and feel ok about things at this point.

sealing the upper deck is an awesome idea....that will be a fix it and forget it modification..with nose and pole foam you will be fine...

pingpong balls dude...

you joke, but it would work great so long as the tray was properly reinforced....I'd use 1 and 2 liter bottles though

I didn't see or don't remember your old thread, that is interesting.

I honestly can't recall that I've ever completely sunk a ski before, though I've helped bring in others. I know it can happen though.

you never sunk a ski living in Hawaii???


sinking a ski can be nothing more than going off for a stab, having the hood come unlatched and before you know it she's sinking despte bilge pumps

without nose or pole foam my 367lb ski would float a couple of inches UNDER the surface and bob down out of sight.....You'd have to tread water next to it and hold it to keep it above the surface

Never have sunk the fx1..I attribute that to the foamed pole and hood desgin....In fact, it wont eben flip upside down...the pole will right the boat lessening its chances of getting swamped

 

[SuperJETT]

you never sunk a ski living in Hawaii???


sinking a ski can be nothing more than going off for a stab, having the hood come unlatched and before you know it she's sinking despte bilge pumps

without nose or pole foam my 367lb ski would float a couple of inches UNDER the surface and bob down out of sight.....You'd have to tread water next to it and hold it to keep it above the surface

Never have sunk the fx1..I attribute that to the foamed pole and hood desgin....In fact, it wont eben flip upside down...the pole will right the boat lessening its chances of getting swamped

I know all about how easy it can be to sink a ski, just can't remember that I've ever done it. Maybe on the 550 in Hawaii, but I really don't remember every doing it, though I've helped tons of people resurrect their's after it.

 

[Flat Brapp]

I say go for it! Your idea seems positive to me.