Yamaha 784cc into welded mod-v hull


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After hand tracing a squiggly orange line onto the laser line, I used a stick to clean up the curve.


The black line on the right, on top of the squiggly orange line is what I'm cutting. The squiggly black line was when the laser wasn't centred properly :eek:


I also slipped a piece of sign board in between, and traced the line onto that. So I have a template for the other side. And a permanent record in case I want to try this again. That's what the dirty white wedge next to the spare helmet is.


Next, have to gather up my nerves and cut it all out using my cordless circular saw. Then notch the corner seam so I can flex the side panels to meet the bottoms, then mark out the filler panel where the chine curves up the bow. But I'm getting ahead of myself here. Gotta tidy up the space, and mark and cut out the transom piece.

See you on the water

I learned a bunch about cutting thin metal sheet. It needs to be secured and rigid, because when it flexes the saw jumps around and kickback is somewhat dangerous. I'm glad to have all my fingers still.

Replacing the 32T non-ferrous metals sawblade with a 60T oshlun non-ferrous sawblade helped a lot. Along with a small amount of lube, and properly securing the material so that it is as rigid as possible did the job. Felt like I was cutting plywood, other than the noise. Bonus, it smells like buttered popcorn when I'm cutting. Cooking spray is easily cleaned up before welding, and apparently traces of it won't contaminate welds as much as petroleum based lubes.





With the centre seam cut-out complete, I couldn't wait to bend up the nose to see what the boat will look like. It's temporarily held together with a strap so I can visualize it.



I'm pleased with the progress this weekend. Next I need to find a helper to roll the hull pieces so I can cut the side panel. Then roll over again, and mark the rest of the nose. I will likely need to tack some braces in place to maintain alignment while I lay out the rest of the nose, so I'll need to get some 2x2 angles or similar stuff. Then I can mark out the transom and firewall and cut those out as well. I'm very happy with how simple it is to cut the aluminum this time around. First try was scary with the kickback. The Oshlun blade is awesome, and affordable too.

See you on the water!

Upon bending the sides of the nose inwards, I found that the upsweep meant that the bottom panels didn't rise enough for my liking. Originally, I had planned to level the nose and have a completely flat front deck, level with the sides. But after seeing the upsweep, decided to try keeping it. For now.



I decided to raise the bottom panels further up for more upsweep. I notched the centre seam panels further back another 1.5ft and had another look. Trimming both sides the same turned out to be an interesting layout nightmare because I no longer had the original square end as reference point. Would have been much easier to make the notch bigger the first time. But I think it turned out okay the second time.



Still have to make space to dismantle the waverunner, so I can measure the engine and jet drive layout, and build the jet inlet.

See you on the water.
CedarRiverScooter said:
Is that a vintage Miata in the background?

Your boat is going to look great!

Hah thanks! It's a vintage ae86 corolla. Not mine, but very much like my old car. We take these old beaters to the track and have some fun. Some guys set them up for drifting, but that's not really my thing.

My old car was very stock looking, but far from stock.

A bit more progress today. I'm not ready to weld quite yet, need to finish layout and cutting first. So to keep the hull rigid for proper layout, I had to make a specialty clamp to hold the hull chine to my work cart/jig.


The other clamp I made is to hold the gunwales in alignment so I can flex the nose and bend it all up.



Need more clamps! Just like horsepower, money, speed, the answer is always MORE!


The nose curve looks fair...


Once the nose was rigid, I could properly lay out and mark up the nose. I marked the inside of the starboard bow area with chalk. Note the faint green line. Much easier to undo temporary chalk markings vs sharpie marker.


Next I used a stick to clean up the chalk line and mark my cut line with a sharpie. Well, a fiberglass sand flag pole.


And then screw the sheet metal down to a 2x6 for rigidity and to make a safe clean cut. Screw heads were countersunk, then buzzed with grinder to ensure no high spots to catch the saw base.





See you on the water,

Sharpie is a lot easier to work around. Erases from the surface of the aluminum with denatured alcohol on a rag.
The bow rise reminds me of the style you see on a airboat.
eshaw said:
The bow rise reminds me of the style you see on a airboat.

Technically, I believe the hull style I'm building is called a Garvey. But I've added chine flats for some grip in turns, as I won't have a skeg hanging below the hull.

As for sharpie vs sidewalk chalk, I used both. The sketch line with chalk was easier to manage, just so I could see where things were going. Once the batten was clamped down to fair the curve, I marked the cut line with sharpie.

Honestly, I wish I knew what I'm actually doing. So many times I've felt that I'm in over my head. The tricky parts are yet to come.

See you on the water,

Before you clamp up the seams, scrub the heck out of them with a strong solvent to remove the sharpie ink.

I mistakenly used a whiteboard marker (only cause it was just laying around) & even thought I wiped it off / wire brushed, it made my welding very difficult.
Thanks for the tips guys. I finally have some progress to share.

I found out my buddy had a welder in his garage. Wasn't his though, so I had to find our mutual friend, and talk to him about selling it.

"Sorry, it's not for sale."

"Well, can I borrow it?"

"Sure, use it as long as you like. If/when I need it, I'll let you know."

Wooohooo! Free welder! Not sure if he's ever getting it back though. So first thing I do when I get it home is to build a cart for it using an old engine stand and some random scrap, plus some swivel casters.


Then I added some MIG gun holsters on the side, for convenience, and the second one for 'storage' position. Yep. Built a cart for a welder that I don't own. Silly, but way better than lugging a welder around, and worrying about tipping a gas bottle. It's a Lincoln MigPak 180, a basic 220v welder that you can get at Home Depot or other big box stores. Doesn't have continuously variable voltage, but does have variable wire speed.



I installed a new liner, tossed out the fluxcore wire and liner it came with, and installed an 035 contact tip to match the 030 wire. This 180 uses the same consumables as my SP125 so I didn't need to buy more stuff!

Then I started tacking up the hull.


And of course, have the magic eraser to deal with the mistakes



I marked up the transom using CAD. Not autoCAD but BoatCAD. Cardboard Aided Design.



There's not a lot of freeboard in this design, but it's a full height transom. I
should just have enough side height to clear the engine. Might have to add a bit with some pipe on the gunwales.

Also started tacking up the nose, and making the filler panels. Then got carried away and started welding the nose seams.


Was happy and excited that I didn't have feed issues with the Lincoln MigPak 180 and a new liner. Voltage and wire speed settings are at maximum. Can't believe I tried so hard with the 110v unit before using the 220v one. Now I have a separate welder for steel and aluminum. Haven't pulled the pin to get a spool gun yet. I'm stubborn like that though. Some of the welds are covered with black soot. Welding aluminum is nasty stuff. Even with a filter mask.

Also quite pleased that I haven't had to use a lifeline and "call a friend" to come weld this thing so far.

See you on the water,

Well these past couple weeks have been somewhat productive. I managed to take the hull off the cart/jig and put it outside in the rain on my trailer. I have it nose up so that it doesn't fill up with water and bend before I put the interior framework in place. I also managed to get the ski inside so I can take it apart. First order of business, remove the pump and check for wear and damage. Also confirm pump size at 155mm.




I need to strip the impeller shaft so that I can have it shortened and re-splined. I did talk to a machinist that does this sort of thing, but he needs to see the bare shaft, to see if it can be modified with the tooling he has.

It turns out that you need two special tools to remove the impeller from the shaft. 1-1/16" wrench, and a spline tool to hold the shaft in a bench vise. To remove the shaft from the stator housing you also need a hydraulic press. The special spline tool is available from various sources for US$11 and is only a few days away if I lived in the USA. But in Canada, there are not many local options. I was ready to order off eBay and wait for shipping, but lucky for me the local boat shop has the required Yamaha spline tools.

NOTE: the impeller is left-hand thread. So to take it off you have to pretend to tighten it! It's also quite tight, probably 100+ ft lbs torque. Properly secure the spline tool in the bench vise, slide in the shaft, and with the stator housing well supported, yank on the wrench. Being a little guy, I stood on the bench and stomped the wrench to crack it free, much to the amusement of the techs at the boat shop. I'm so lucky they let me do my own work. I spoze it's free entertainment for them.


I still need to press the bearings and sleeve off the shaft, but it's at the point that it can be measured. And easily transported.

With the pump out and apart, I pulled the engine. Remove exhaust pipe (again) to access the throttle and choke cables. Remove fuel lines and oil supply line. Cap oil reservoir so I don't lose a gallon of oil into the bilge. Removed the carburetor to reduce chance of impact damage. Removed power valve control cables. Unplug ignition control box from instrument panel. Unbolt mounts and lift out engine.


Made a small cart to make it easy to tuck the engine into a corner. Re-installed carb, airbox, and exhaust manifold so I can measure the package. It's 22" tall. 22" wide. And a tick over 19" long not including the exhaust. Weight is about 120lbs but I don't have a scale to properly weigh it.


Next weekend I plan to disassemble the rest of the ski and maybe take the upper cap off so I can properly measure the engine mounts and figure out how to make the pump inlet and engine mounting rails out of metal.

See you on the water,

Back from the archives :eek:

Haven't done much in the last several months until this week. Honestly didn't think the boat would take this long, my friends are now calling it my "five year project." I've lit too many fires, and have to focus on what's important: the boat.

The water inlet is a big hurdle. If I get it right, boat will be fast and sweet. Get it wrong, and I'll have to re-do it, or spend $$$ buying one. First step is to actually take a close look and measure up the stock waverunner water inlet. So I cut up the hull to remove it and mock things up. Cordless tools are great, but the number of batteries you need is always at least one more than what you've got. Cutting this beast up took all morning. I had to borrow a big battery from my neighbour too. And use his charger so that I could charge two of my batteries at once.






That piece of plastic is HEAVY. Probably 60-70lbs of plastic. Looking at it, a glue-in won't really work well. I'll need to make the inlet out of metal, and had a piece of sheet bent up to clear the center weld and make a cassette to drop in when complete.


With the water inlet in a manageable size, I could now measure and attempt to duplicate. Dang this thing is more complicated that I envisioned. The shape profile starts off rectangular, then goes to round. The removable shoe and grate shape is complex as well. And dirty cast aluminum will be difficult or impossible to weld.





a long road ahead still.

See you on the water,

My welding mentor says it may be possible to weld the cast, but I'd have to pony up for some more equipment, an AC TIG machine. And learn to TIG. I will likely tack it together and then use the "call a friend" lifeline and get him to weld the whole water inlet. Haven't got there yet, still measuring and mocking up. Also need some more 1/4 plate. And build a jig to hold the whole thing in alignment.


Time for more CAD. Cardboard Aided Design.

The dirty water inlet shoe. Will need to cut out most of the outer housing to allow the actual shoe to be integrated into my cassette. Then once this is all together, weld the cassette into the hull, build the motor mounts and transom, etc.

more or less where it would sit.

I asked my other buddy if I could buy or borrow his AC TIG since he hasn't used it in a while. Yay, it was for sale, so I took it home and immediately built a cart for it using whatever was laying around. The back wheels are from a broken kids scooter, and the front swivel casters were laying around from a previous project. Everlast PowerTIG 185DV. I'm looking into stubby gas lens kit as well as a watercooled torch, but that may not be required for this hull. Good thing I had two 220v/20A outlets installed at the same time. Now I can have both MIG and TIG powered up and plugged in. Will need a second 220v extension cord though, when funds permit. Have already ordered up a TIG finger heat shield and some thin TIG gloves, just waiting for delivery.


My practice beads look much better than the MIG welds. Will have to run over the MIG to see if they improve, otherwise will have to cut it all out and redo at some point. Probably after water testing this bad boy.

There's a long road ahead. Hopefully this long-weekend will net some more progress.

See you on the water,

Looking good! Mine took a long time to build too, but the end result is worth the effort.

I never fully mastered aluminium welding, so I ended up with pin holes, particularly at weld stop craters. I gave up trying to perfect that process & sealed the welds inside the hull with 5200 plus covered the outside with epoxy resin/fiberglass cloth.

The latest addition to my boat is a winch mounted at the bow - the last 2 times we went out we ran up on gravel beds (obviously not paying enough attention). Fortunately we were able to lift it off, but next time I am better prepared!

Keep the photos coming!
CedarRiverScooter said:
The latest addition to my boat is a winch mounted at the bow - the last 2 times we went out we ran up on gravel beds (obviously not paying enough attention). Fortunately we were able to lift it off, but next time I am better prepared!

Can't wait to get stuck on gravel bars. Hoping that a slick bottom coating makes life easier. But that will be after the boat gets in the water. And I'm still a long ways from that yet. Still figuring out how to put it together at this point.

Getting some arc time in with the TIG welder has been fun so far. So much more control, but I haven't figured out how to smoothy add filler rod yet. I've got both machines plugged in to separate circuits, so I can use both MIG and TIG at the same time. Both grounds connected to my table. Just farting around at this point with the machines and the process.

The Lincoln MIGPAK 180 has a ptfe liner now, and feeds smoother than ever before. With proper prep work, it's much faster, but the welds don't hold a candle to the TIG welds. Now if I could only see better with my old set of eyes, and dab filler smoother, I might just get this boat together.



I'm excited that I'm finally getting back at working on the boat.

See you on the water,

Well I'm slowly plodding away at the water inlet. In the meantime, I did find the service manual for the waverunner here:


And it's been quite useful so far. I'm trying to put the engine as far back as I can, to increase cockpit space in the boat. The plan is to shorten the driveshaft and the intermediate shaft. And intermediate shaft shortening requires disassembly. The service manual is helpful for that. Short story is that the shaft is pressed into the bearing, and the coupler is threaded in place, and retained with pipe sealant.

Also found the parts catalog for the waverunner here:


Apparently the 1100 waverunners use a shorter intermediate shaft. Make sense, as the triple cylinder engine is longer. But the couplers are the same, so I could use the 3-cyl shaft to move the engine back, and not have to shorten my 2-cyl shaft. If I can find a used one. But I may be able to shorten the 2-cyl shaft even further to move the engine further back by an inch or two. But that's a tomorrow problem.


Sounds like you are enjoying the analytical phase of the project.
Maximizing cockpit room is a worthy goal.
Keep the pictures coming!
A couple musings of that engine (XA800).

They are kind of peaky even with the power valve system. In other words, kinda hard to vary the power, beginning at about 1/4 throttle. From there, you are at maybe 25% power, but at half throttle you may be at 75% power, kind of like an old 2 stroke dirt bike. I always liked them but they weren't real smooth in power delivery in the factory installed application.

Secondly-if you decide to test run out of the water, you get about 10 seconds. Once the spark plugs begin to glow (and they will), it will literally diesel, you can't shut it down. The first time this happened to me on a ski what was started without water in it, I about pooped my pants...brand new unit, couldn't get it shut down, was sitting there running. I pushed the stop button. Then removed the lanyard. Then both plug wires pulled off,still running about 6000 RPM. I had no idea what to do. After maybe a minute, during the time I was trying to get to the air intake to starve it, I reached over and pulled the choke knob out, which then killed the motor. No telling how hot it got. To my knowledge it never did show back up for any engine troubles so maybe it was ok. I mentioned the issue to our then yamaha rep, he said that the 800's and 1200's were susceptible to this from time to time. They also said that the 800's especially were really "peaky" in their design and that some folks would probably complain about it-and they did. But they were fast.
Todd, thanks for the insight.

Re: runaway engine, I've definitely experienced this. Pulling choke out did shut it down.

I thought I'd have more time to spend on my project, but alas it's been over two years now. At some point I need to finish the water inlet. I probably should have bought a cast unit instead of ghettofabbing my own, but hey, hindsight is 20/20 and is for helping out the next person in the same situation. We shall see.



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