Flathead's Combee TomCat

[buster]

Flathead,

That's coming together real good. I especially like the diamondplate on the transom. That looks sharp.

Hope it performs as good as it looks

Dave

[Flathead]

Dave,

That diamond plate IS the transom. I left enough of the original fiberglass to maintain some structural integrity, but the diamond plate in the only thing between me and davey jones locker

Bruce

[whobbies]

Bruce, I ran into a similar situation with a 1725cc VW mid-engine in one of my trikes. I installed a 10" automotive electric fan under in the center of each bank of cylinders and it solved the problem. Being I to am in the middle of restoring the exact boat as yours, I am now concerned with what you have been experiencing. The guy who sold me the boat told me it ran great, but was in pieces when I got it???? It came with an adjustable composite prop set at 23 degrees pitch, I hope all this effort will be worth it? I'm going to try to find the origional designers, they are in my neck of the woods for some input. I know a couple well know air boat builders that may have some leads.
Tony

[whobbies]

Bruce, I should of read on, and now noticed that you converted to the Rotax engine. Were you able to get the VW engine to perform the way you wanted? I am now trying to decide what way to go with mine, any advice will be appreciated.
Thanks,
Tony

[Flathead]

Hey Tony,

I will be glad to offer any advice/insights/observations you may find useful.

As you read through the thread you will get a pretty good idea of how the Fatcat performed with the VW engine. It sounds like your goals and mine, as far as performance are concerned, are similar. I wanted the Factcat to be able to get on plane hauling two people and a modest amount of 'gear' in deep water. Frankly, it never did. Just too heavy and not enough hp.

I would bet you will end up with a similar result if you go with the same 1600cc dp engine I was using.

I was left with the option of spending a great deal of money for a reduction unit to try to get better performance, using a larger VW motor, or scrapping the whole VW motor idea and going with something else. My choice was obvious, and so far I've been very pleased with how it's turning out.

Having said that, I'm the first to admit my experience with VW motors before the Factcat was exactly ZERO. To this day I'm not sure I ever had it tuned to give it's rated hp. Plus, using a direct drive, the prop speed is limited to 3000-3200 rpm's or so therefore that's all the rpms you can run the motor at. Those Tomcats were originally built using VW motors(at least some were) so I would tend to think mine may have been a little weak.....

Anyway, if you have any question just ask or send me a pm.

Good luck

Bruce

[Bogger2]

Hey Flathead,
It's looking great! I bet it will scoot a long real good with the Rotax, Mine does. Keep us posted when the testing comes up.
Bogger

[Flathead]

Update time. I got my new warp drive prop installed and the pitch pretty well dialed in. The prop is 3 blade, solid carbon fiber, 68 inch dia. I must say the workmanship is excellent and it's ridgid as can be. Hopefully, when something else goes thru the prop, it won't ruin it. (note I say 'when' not 'if')

It's running real good, the only problem is the little boat starts to porpoise at about 24mph. So today it went to the lake with about 70lbs of weights to see if I could get the bow down a little. After a few trial runs I found about 60lbs in the front helps. I was able to get up to 31mph on the gps before porpoising started. I thought that was promising.

Next I'm going to adjust my prop angle a bit and see what results I get. It's coming together quick. I've got my seats back from the upholsterers and they look pretty good. I'll post a pic once I get them installed.....

BTW, A note to any of you other Tomcat rebuilders out there who may be planning on using a VW motor: Water washing over the transom (and sides) is a real issue. Be aware. I even added 3" of height to the fatcat transom and I still get some come over once in a while......

Bruce

[Duane Scarborough]

Flathead,

I'm glad to hear that it's coming together nicely.

Looking forward to the pictures.

The Warp Drive props are supposed to be tough as nails. The only negative thing that I've heard about them is that they can be fairly LOUD. But I'm sure that how loud depends on a lot of variables. (# of blades, pitch, prop speed, etc.) Granted, a lot of the noise related info has come from very high HP boats with high blade counts.

How would you rate your installation, as far as noise level goes?

Good luck with it, and keep us posted.

Duane

[buster]

Flathead,

You would have to rain on my parade, just about the time I'm ready to bolt in my VW engine mount Do you think it would help to move the engine forward a few inches? I really don't care to have it run on its' nose, but there must be a happy medium.

Let me know if you have any ideas about that

Thanks, Dave

[Flathead]

Duane,

As far as sound levels go, the original ultra prop was the loudest, but it was spinning the fastest, back when I was running the DD VW motor. The next prop, the powerfin was considerable quieter, and I have noticed no difference in the sound level now that I am running the Warp drive. I wish the manufacturers would publish the sound levels their props produce. It seems like it would be relatively easy to measure.....

Buster,

Before I modified the hull or the tomcat, and was running the VW motor, I did not have any porpoising problems. Of course my top speed was only 26mph or so. What you'll get with you bigger VW motor and higher speeds, who knows. I tried moving the motor up a few inches and got no change in performance....

Flathead

[Flathead]

I was finally able to get the boat to stop porpoising at high speeds. I ended up bending down the trailing edge of the boat bottom to form a small trim tab. Runs out great now. No hint of porpoising at all. It rides on its nose just a tiny bit but that's OK. I can live with it. Still having trouble with belts slipping on my redrive, but only at high rpm's. I can only tighten the belts by shimming the motor up and that's a pain, so I'm going to change to a 'screw jacking system' it will make a good winter project....

The Fatcat gets on plane pretty good too. It will get me and two others (about 600lbs.) out of the water and cruise without having to push the motor to it's max. Two people and a cooler, no problem.

Today at the test run, I saw 31mph at 5500rpm's. It cruises at about 23-25mph at 4500rpm's. Belt slippage prevented going to the full 6500rpm max.

The only thing I plan to change is the peaky nature of my 2 stroke motor. When I give it gas the motor smoothly increases rpm's until about 5000. Then, lookout, it's like hitting the nitrous button (or second gear as my daughter puts it). The motor just screams, rpm's shoot right to 6500 or so and it really puts you back in your seat. The boat jumps out of the water. This by the way, is when the belts tend to slip. I'd gladly sacrifice some peak hp for a better midrange. I may play around with tuning my exhaust a bit....

Here are a couple of pics of the boat as it is now. Now that I'm confident it will run reliably and safely, I can get busy finishing up the details.....always details....

Flathead with a Fatcat

[buster]

Wow, a boat that jumps out of the water, that's a problem some guys would spend lots of money to have!

The Fatcat is lookin' real good with the new upholstry etc.

Dave

[Bryan61]

I had a vw dual port I think it was a1973 rebuilt with a 52'' two blade I think the pitch was 28 { it was stamped on the prop] but I could only turn it 2700 rpm and the people a arrowprop told me about 3200rpm But unfortunetly it flipped over when i was turning without any prop speed and the river was very high.

[Bryan61]

my jet ski would porpoise at full speed when there were 2 people on it but with one it would not so mabe it would help but i"m no expert

[Bryan61]

that a nice looking yellow combee tomcat, I'm trying to find a small airboat hull so I can get away from my plywood hull but in Iowa there just arent many around and a new 10' lund jon boat is about 480 dollors

[Flathead]

So, after some research, I've decided my motor is not 'peaky', rather it has a flat or dead spot around 4500rpms where it does just not respond to changes in throttle settings. Might be carbs, might be exhaust tuning. details, always details.........

Bruce

[buster]

I have heard that those 2 cycle engines are real fussy about exhaust backpressure etc. Do you have the stock exhaust-muffler, or a homebrew setup?

Dave

[Bryan61]

I have heard that those 2 cycle engines are real fussy about exhaust backpressure etc. Do you have the stock exhaust-muffler, or a homebrew setup?

Dave

No its got a small supertrapp muffler

[Flathead]

It's a stock exhaust. However I did have to change the angle of the bend in it to get it to fit. I changed the angle of the bend by cutting out a pie shaped wedge and then welding it back up. I would guess I shortened the expansion chamber by about 1" give or take. That's why I think I will look at the exhaust tuning first. fortunately I have another stock, non-modified pipe to try, if I can get it installed, even temporarily, without modification......

Bruce

[Flathead]

Well, that made no difference. Had the same flat spot at the same rpm's. Next I will look at my carb jetting. I did change it from the original snowmobile setting to run in warmer temps. Maybe I'm a bit too rich ( or maybe too lean...) details, always details.

Flathead