Yamaha 784cc into welded mod-v hull

[86tuning]

Boat hull has been yard art for a long time, and I've been procrascinating because I'm stuck with the water inlet still. So I made a jig to hold things while I sort it out. I'll be using the cast pump shoe and grate, but need to make the upper portion out of metal. And the shape is complex enough to stall progress. But simple enough that I'm too cheap to buy a commercially made cast water inlet.





Next, I examined the cast pump shoe to determine which portion I need to save, and which portion to delete, and how to go about cutting it. I do have a hack saw, but hand tools are for chumps



I managed to clamp it in my vise, and hack it off with the circular saw. I managed to keep all my fingers too.



A lot more trimming is needed, but this at least is a reasonable start.



Next step is to mark the outer hull before I get too carried away building the powertrain cassette.





Then back inside to build the water inlet.



Clamping the pump shoe is still tricky. There aren't any strong parallel surfaces for it to be held properly in the bench vise. So I had to improvise, using ancient woodworking technology: the holdfast. With no moving parts, these clamps were designed centuries ago. With it held securely, I was able to use the carbide burr on the die grinder to trim it. Then a vixen file to (hand!) finish the edges.

 

[86tuning]

So I'm building a flat ride plate under the pump shoe, not the original vee plate from the jet ski. The ski hull is deep-V of about 18deg and my hull is 10deg. A flat ride plate is the simple solution. Many modern jet skis and boats have a flat ride plate. I used a piece of 1/4" plate for this and managed to overheat it and warp it.



As you can see, the ride plate has tipped down 5 deg or so due to warping of the assembly after overheating it.



Lucky for me, when I cut out the ride plate, the cassette went SPROING and sprung back to flat. So I made another one, and was careful to not overheat it this time. MIG welds look terrible before wire brushing



Next up, the pump mounting plate needs to be mocked up and cut out of 1/4 plate. During final assembly, when the 1/8" transom is added, the mounting plate will be 3/8" thick and should be plenty strong. More cardboard, because cardboard is easier to cut than metal.



Ancient sabre saw with a dull blade. Sourcing supplies is a bit problematic at this time, it would be at least 1/2 hour line up to get into any stores to buy blades. So, just muck around with what I got. Also, I'll be running a bead around the cutout so smoothness isn't a high priority. Plus, I can always clean it up a bit with the die grinder if required.





All these pieces are awkward to clamp, so temporary assembly and tacking makes more sense. Tack welds are easily cut out to disassemble before final welding all the inside pieces.





And now the tricky portion that I was actually stalled at. How to make the curved portion symmetrical? It's hard enough to make out of cardboard and mark up, how the heck can I make this out of metal? Yeah 1/8" stock can be bent by hand but I want 1/4" plate for rigidity and strength. And to deal with future pebbles.

 

[86tuning]

Doesn't look terribly complex when mocked up in cardboard.



Now to cut out a couple pieces in 1/4 plate



To bend it, I considered scoring the outside several times, making a shallow groove and then forming it by hand. Then welding up the grooves for rigidity and strength. In the end, I figured out how to make a press brake using a 2" piece of round stock at the top, and a piece of angle iron for the bottom.



One side at a time, running back and forth between the hydraulic press and the inlet jig.



Then make the other side, and fit it all together. The interior shape and dimensions of my water inlet closely mimics the shape of the original plastic water inlet from the waverunner hull. I figure, if the engineers spent time to design it, and it works, why re-invent it? Yes, I do realize they had design constraints as well. The plastic hull needed to be easily formed in a mold, and that's why the pump shoe bolts in. But I assume that the overall shape of the water inlet must be optimized for performance already.





And that's what I've been doing for the past while.

Next, the upper inlet plates, and then disassembling the entire unit to weld the interior pieces and make this into one piece of aluminum. Welding the cast portion is not going to be fun at all. I will be welding, then grinding out the contaminated weld, and re-welding a few times to fuse it properly. Then grinding and shaping it again.

Once it's together, I'll be bolting up the jet mounting plate, then mounting the jet, making the hole for the impeller shaft, the shaft bearing coupler thing, then shortening the impeller shaft and re-splining it, so I can get the engine closer to the transom. Then building motor mounts.... so much more work to do. But at least the tricky part of the water inlet is almost done.

One day I might be able to float test this thing....

 

[CedarRiverScooter]

Nice craftsmanship! I esp. like the forming technique.

 

[86tuning]

Thanks Cedar, it took a lot of overthinking to figure out how to form the 1/4" plate. I burned a lot of brain cells working it out. Then finally decided that I just had to "measure once, cut 10x" and try. And it came to me the next evening.

Next step is to mount the pump unit and figure out where to put the coupler. I temporarily hung the mounting plate in place, and marked the thru holes.



Make holes in plate for thru fasteners and fittings. Then secure the mounting plate.





There's a lip on the mounting plate due to the previous location, where the plate mounts under the u-shaped water inlet in the ski hull. Since mine is now mounting through the transom, I need to remove the lip to sit the mounting plate flush with the transom.





Then re-install the mounting plate. Next, I have to reassemble the pump so I can poke the impeller shaft forwards to see where it sits and where to put the coupler. So I dig through a bin I haven't looked into for about a year.



What is this black ring? where does it go? Dunno, will have to look in the service manual and exploded diagram to see where it goes....someday soon.

I manage to partially assemble the housings and slide the shaft forwards for a look. And a pic or two.




The location of the coupler dictates where the engine can sit. I would like to put the engine further back to maximize cockpit space in the boat. I can live with a smaller rear casting deck and less covered storage if I can have more room for driving and seating and moving around the boat.

I put the original plastic pump housing and stuff next to my metal one to figure out where I can put the coupler. And how much to shorten the impeller shaft. Also, will need to phone around to a few machine shops to see who can cut the splines, because my machinist buddy isn't set up to do splines.









Looks like I can move the engine back exactly 6" so I'll need to either buy a 24" shaft, or have this one shortened from 30" to 24"

This week I need to weld the pump shoe and the pump housing together, and find a machine shop to modify the impeller shaft. Then I get to start the engine mounts.

Cheers,

Brian

 

[CedarRiverScooter]

Looks like you will be getting lots of welding practice!

What will you use for the shaft thru-hull fitting ( AKA 'log' for an inboard)?

One thing that haunted my boat is not getting the pump angle right. If you have power trim, ten it should be no problem.

I just got a pump wedge for mine, I was getting porpoising at anything over 30 MPH.

 

[86tuning]

What will you use for the shaft thru-hull fitting ( AKA 'log' for an inboard)?

One thing that haunted my boat is not getting the pump angle right. If you have power trim, then it should be no problem.

The stock impeller coupler has a bearing and seal. No different than what's done with the ski hull. Only difference is that I'm integrating the pump shoe into the hull instead of the bolt-in style on the ski.

The pump does have trim, and I am concerned with efficiency, but there are too many variables to consider for drivetrain angle. So I'm running 'stock' 2 deg down for the pump. I hope it works. Also, planning on putting the fuel tank in the nose so it can be on centerline. Plan B is to put it inside the centre console, but that makes the console a lot bigger than I want.

The bottleneck is to find a machine shop to cut small splines. Everything is dependent on it. Coupler position, engine position, yada yada.

Cheers,

Brian

 

[eeshaw]

Another option other than machining splines would be to cut the six inches out of the shaft and have a sleeve slipped over the cut and secured in place. I've pinned axles like this. You can weld the sleeve or pin them in place, but if you pin it use tapered pins and peen the end so it can't back out.

 

[CedarRiverScooter]

+1 on cut & splice. I would just add that heat shrinking the sleeve on would add some strength. A woodruff key is pretty easy to machine in too.

Probably not germain to a jet ski shaft, but years ago we cut down a Ford 9" differential for use in a sports car (Sunbeam Tiger). The half shafts were cut & resplined. Bad advice from someone, said to use them as-is without heat treat. After about a year I had them out for some reason & clearly they were twisting. I had to pay thru the nose to have them induction hardened. But at least that worked.

 

[86tuning]

Haven't done much recently. Have called all the local machine shops to find out who can cut small splines. The machine shops I regularly deal with don't cut gears and splines. The two closest gear shops don't do small stuff. They're all referring me to other shops. MiniJet Inc can cut it, but I would need to ship the shaft to the other end of the country and back again. Would rather spend local if I can. Monday I'll drive around to a few gear shops to see if they can do the job. I'll know in a few days.

I'd rather not cut and weld the shaft, since MiniJet can shorten and respline it, I should be able to get that done locally. MiniJet's website charges cad$200 to shorten and respline the shaft, and there is no mentioning of hardening, etc. I figure I'll just bring the shaft and coupler so they can make sure it all fits back together properly.



These are the smallest drills in the set. 5/64" on the left, 1/16" on the right. Shaft diameter is 20mm so a hair over 3/4"

I have to remember to mark the outer hull for the grate and the ride plate before I weld the whole thing together. Marking it now will be a lot easier. I should probably cut out the water inlet in the main hull as well.

Next, I'll be finishing up the water inlet at the same time. Lots of welding and reinforcement to the pump shoe area. Also need to mount the coupler section, after I reassemble the pump.



Cheers,

Brian

 

[Jim]

I am in awe man. :beer:

 

[86tuning]

I am in awe man. :beer:

Haha thanks Jim! I'm grateful for the opportunity to blog my build here on TinBoats.net. It's taking forever...maybe I'll finally get it wet this summer. There are so many people and resources here that have helped me get started. Would have been a lot harder to take the leap if it wasn't for TinBoats.net

Cheers,

Brian

 

[86tuning]

Well I tried several local machine shops and gear cutting shops, nobody wants to tackle this thing. They're all referring me to each other's shop. One gear shop tested the hardness and determined that their HSS cutters won't cut the material. The other shop said they didn't have a cutter for the JIS splines, but even if they did, estimates that this is likely a $1000 job. Which is a complete deal breaker.

So I'm sending the shaft across the country to minijet.INC to have them modify and send it back. They want the coupler shaft as well to confirm fitment, which makes it more fun to package up. Either I send two packages, or make some big package to ship the coupler with the shaft.

Instead of sending the whole coupler, I decided to disassemble the coupler shaft and simply send the splined portion. So I need a coupler wrench, which isn't hard to obtain, but I don't want to wait for shipping and customs to get from the USA.



DIY coupler wrench. I made it out of 1/4" aluminum instead of steel so it's softer, but needed a strong drive section. So I used a lugnut, and welded it to a backing plate. Then put some random beads in the aluminum to prevent rotation. I don't recommend this, instead simply buy one from Greenhulk or any of the other jet ski suppliers. Or better yet, have a jet ski shop r&r the coupler for you.







Now I don't have a holder, but since the shaft will be shortened, I can use the existing splines to hold the coupler. To keep it from turning, I welded a bump on the shaft. The couplers are on quite tight, and are retained with Loctite 572 pipe sealant.



Thankfully I have a good impact wrench, and it made removing the coupler simple once I had made the special tool.





So now with the shafts in a more manageable size, I can slide it into a piece of plastic pipe and mail it.







And it's off via parcel post. Not sure what shipping is going to cost, but at least it's on it's way. Might even see it back before the end of the month. I've asked they return the cut off section to me, so that I can use it to reassemble the coupler, and not have to buy any more special tools.

Cheers,

Brian

 

[CedarRiverScooter]

Quite ingenious! I make my own pullers too, sometimes they even work :wink:

Glad you found a shop to rework the driveshaft.

I suspect the carrier bearing on my jetjon is bad (VX110 engine). I think it is same coupler. So don't junk your tool just yet, there may be a buyer for it.

Something in the drive train is binding up & I suspect that bearing. Unfortunately, I have to lift the engine just to check it.

 

[86tuning]

I suspect the carrier bearing on my jetjon is bad (VX110 engine). I think it is same coupler.

Shouldn't need to unscrew the coupler from the shaft to change the bearings. They're press fit, and you should be able to have the bearings replaced without pulling the coupler off the shaft. Getting it apart is another story, if the pump and shaft are slid off the back, maybe the coupler assembly can come out? Not sure, I'm not a jetski tech and have zero experience.

If you need a coupler wrench, I recommend buying one. It's about us$28 from quite a few sources. You'll also need a spline tool to hold the coupler shaft, which will be available from the same sources. I just didn't want to wait, and had materials here to make one. Shipping times are quite uncertain these days.

Cheers,

Brian

 

[86tuning]

My materials have arrived from the bending shop. Almost have everything I need, other than the impeller shaft, which is still in transit to the machine shop according to the post office. It's been one month now, and their delivery date is to be determined which I hope isn't a euphemism for "lost."



The walk-around gunwales I had in mind will do three things:
1. allow walking around on the gunwales (duh)
2. increase structural integrity of the hull with the large box section
3. add some flotation to the hull, as they'll be sealed and pressure tested

I hope it works out the way I envisioned. Temporary mock up to check fitment.



The other pieces are floor stringers to support the cockpit sole. It's actually high enough to almost self bail, so I may install a plug on the side of the hull, and/or scupper valves. But that will wait until after the water test.

The stringers are again temporarily mocked up to check fitment. They'll be installed amidships and not at the transom as pictured. The engine bay and motor mounts are completely different design.





The cabin sole will be plug/rosette welded in place, and will be a sealed and pressure tested chamber as well, to offer flotation. Technically, it's not recommended for a hull member to serve as flotation, but if I puncture 1/8" aluminum I have bigger problems to deal with. With just longitudinal floor stringers, if there is impact on the hull it might dent but shouldn't tear. The box shape will impart significant strength and stiffness to the hull as well. Or at least I hope.

Over the next little while I will build the cabin sole and the conduit for the controls and electrics. I hope I don't warp the crap out of the hull, there is very little distortion at this time.

The saga continues....

- B

 

[CedarRiverScooter]

Wow, that is going to be 1 stiff boat.

Maybe you could seal the bottom compartments individually, so a hole in 1 won't mater as much.

BTW, if you rip a hole in hull, it is because you are in shallow water. My wife & I both think we need to have helmets more that life jackets :wink:

 

[86tuning]

Cedar, I never really thought of it that way. Would take a high speed impact on something immobile to pierce the hull, since the projected weight of the boat is well under 500kg. And that would only happen in shallow water. I feel a LOT better now. Because flotation would really only be important in deep water, which I will venture to when I troll for salmon.

Progress update: I managed to figure out the assembly order for the boat. I can't do anything further with the driveline until the impeller shaft is back from the machine shop. So now, onto the hull. It's finally GO time!

Preparing rosette welds. Had to do some more math, because I wanted somewhat close hole spacing, and at the same time, an odd number of holes that I could 'middle' each time I welded. So that would mean 1, 3, 5, 9, 17, or 33 holes. This way I can weld the middle in place, and weld each end, then in the middle of each weld, over and over again to reduce pulling and warping.



the stiffener brace is 82" long, so I decided on 5" spacing, for two rows of 17 holes. Then I drilled them at 1/8" pilots, and then 1/2" final dimension. I happened to have a larger drill bit available to debur and chamfer the holes quickly and efficiently. I've always wanted a countersink bit, but have been too cheap to get one my whole life. lol.



I inspected the inside of the main hull seam for deficiencies. I had done this a year ago, and it definitely warranted inspection. I ground out any craters and signs of porosity, and then re-welded any low spots. A close fit for the hull stiffener is required. Then I started tacking it. First the middle, then the aft end, and now I have a small headache to deal with at the forward end.



The hull begins to curve at the very end of the stiffener, but there's a gap behind it. Might have to drill thru the stiffener and bolt it together. welding a dog to clamp it down seems to be more work than a thru hole. In any case I have to grind out one of the welds at this spot today. Might have to use the lifeline and beg my buddy to come help lol.

In other news, the post office has notified me that my impeller shaft has finally arrived in Ontario after a 5-week journey including the 3-week delay. Now to wait on the machine shop, and choose an alternate shipping method for them to send it back. Yay progress!

Cheers,

- B

 

[CedarRiverScooter]

I would just 'slug' that gap with some scrap material & weld it in place.

Keep in mind you only have yourself to please.

 

[86tuning]

Buddy suggested trying self-tapping screws before thru bolting. So I drilled a 3/16" hole thru the top layer, and a smaller hole thru the bottom layer and put in some screws. Seems to have done the trick. You can see the weld that I ground out in the lower right corner of the pic. It's now sitting flush. When I fix the through-holes, I'll be cutting the top layer to rosette weld at the same time.



With the rosette welds all in place, I started with the stitches on the side of the keel doubler. And then began to add the longitudinal braces. The height and width of these are designed to put a small camber curve into the cockpit sole so that water won't puddle, but rather flow to the sides like street gutters. Of course this depends on boat's list, but I'd rather avoid puddling if I can in the design phase. The idea is that a curved floor will be slightly stronger as well. I'm using .080" for the floor, which is heavier than needed, considering that most tin boat hulls are 1/16" or .062-.064" and with 8" spacing between the floor supports it is a bit overkill at this point.



Also have to deal with some other smaller warpages, and supporting from the bottom is helping. This is the part of the build that's somewhat nerve wracking, trying to keep the hull from warping as I weld. I made an adjustable support to help deal with that. It's working so far, but I have nightmares of putting a twist into the hull. Tying it down to the cart is helping a bit too.





The bow and stern eyes I ordered have arrived. They're cast aluminum, so they'll be a bit tricky to weld up. Might have to switch to 4043 which is supposedly better for cast aluminum.

Also the 135 deg helm unit is here, along with a super-budget 13" steering wheel. I figured I didn't want the 60 deg unit that came with the ski, and 135 would allow me to keep my finger on the throttle. 270 might be easier to steer and less twitchy, but probably not ideal for finger-throttle application. I'll be using 33C or 43C style control cables, like what was on the ski, instead of a steering cable$$ because it's a light weight low power application compared to the 400+hp full size jet boat. I haven't worked out all the cockpit details at this point, but may try a bike brake lever, or else an aftermarket finger throttle. Or might just wrangle something together. But that's a tomorrow problem.





Cheers, - B