Props for Tom Cat

Doryman · Posted: Thu May 22, 2008 3:11 am Post subject: Props for Tom Cat

I'm planning to work with Power Tech to determine the best prop for my boat since I am currently not able to reach max RPM with my current props.

First step is determining the actual weight of a Tom Cat in the water. Has anyone weighed one off the trailer or weighed the trailer with and without the boat?

The more data points the better!

Warren

matt_unique · Posted: Thu May 22, 2008 8:17 am Post subject: Prop/top speed

If I may piggy back with a similar question...

What is your top speed thus far? My engines are installed on the lowest bolt holes, meaning they are as far in the water as possible, and I'm running the 16 X 21.5" props as recommended by Dr. Bob. My top RPM is 5200 so far with a speed of 46 mph, just about 40 knots. The counter rotating engine is to starboard, "normal" engine is to port.

When my boat was sea trialed the engines were mounted on the middle bolt hole, and the max rpm was 5800 in one engine and 6100 in the other. I did not keep it there since the engines had about 2 hours on them so I don't know the top speed. Certainly the position of the engines in the mounting holes and thus trim will determine your top rpm/speed. The inside engine would rev on a turn in the original position and I learned the middle bolt was too high.

I have been wondering if my 2008 engines have more bolt holes than other years? I have a total of 5 holes, and I think Bob for example mentioned he had a total of 4 holes. If this is the case I wonder if mine should be lifted up one hole to increase the rpm? With that, is trimming the engines up farther doing the same thing? I know the vector of thrust would be different of course.

Thanks

Alok · Posted: Thu May 22, 2008 8:37 am Post subject:

Twin counter-rotating Suzuki 150s.

Top speed 45 mph with full gas, water, and bottom paint.

After adding a bimini, Permatrims, and the usual stuff that collects on a boat, top speed is 43 mph.

Captains Cat · Posted: Thu May 22, 2008 9:27 am Post subject:

Twin, non counter rotating Suzi 115's.

Props are 3X14X19's.

Don't recall top speed, it's in the driveway now being serviced.

Charlie

starcrafttom · Posted: Thu May 22, 2008 11:56 am Post subject:

I just happen to have a set of rapture stainless steel 13 1/4 x 17 props off a tom cat that I would like to get rid of so I can afford new props for my honda 90. they list for $247 each and I will let them go for a lot less. I will be putting them on craigs list but wanted to offer them here first.

Doryman · Posted: Thu May 22, 2008 1:25 pm Post subject:

matt_unique · Posted: Thu May 22, 2008 2:11 pm Post subject: Fluids

By the way, my figure above was also fully fueled and with full water.

Wefings · Posted: Thu May 22, 2008 2:26 pm Post subject:

FYI , the Suzukis and the Yamahas have different gear ratios , so you cannot compare prop pitches or diameters between brands . Powertech is a good company with a dizzying array of blade shapes . I would guess you will end up with 15X19 Pitch props. Yamaha's props are excellent but pricey. The Tomcats need a prop with alot of bite and like to be trimmed up as far as possible . Need to know whats on there now..........If Yamaha it will be cast on the outside of the prop . Some props [like Michigan Wheel ] will have it on the inside of the hub .
Marc

thataway · Posted: Thu May 22, 2008 3:08 pm Post subject:

As Marc says, you need to know the ratio of the lower unit and what size prop you can swing. I went with the Suzuki because of the larger props.
I still get well over 40 knots with the boat fully loaded and can achieve 6000 RPM. I have the 16 x 21.5 props.

I run with the permatrims/cavitation plates right at the surface.

matt_unique · Posted: Thu May 22, 2008 3:30 pm Post subject: RPM

Doryman · Posted: Thu May 22, 2008 3:37 pm Post subject:

According to my sales documents the props I now have are 15-1/4 x 17. I will check for numbers next time I am at the boat.

Can I interchange a prop from a Honda 90 with a Yamaha 150? Where can you find out this kind of info?

Warren

Wefings · Posted: Thu May 22, 2008 6:11 pm Post subject:

Just ask on C Brats! No you cant easily interchange as one is hubbed for a V4 size and the other is a V6 size hub .
Marc

Doryman · Posted: Thu May 22, 2008 7:58 pm Post subject:

thataway · Posted: Thu May 22, 2008 8:12 pm Post subject:

I'll answer for Marc--yes as in V4 vs V6 cyliner configurations. There are several hub configurations--some props are interchangerable, but generally these are within the same block size. One exception is the Suzuki 150/175, the 16 x 21.5 are usually for the 200/225 engines, but they fit and do well with the cats, which are more effecient hulls.

Wefings · Posted: Thu May 22, 2008 10:05 pm Post subject:

Bob , if you want a job , we have an opening for you here! The word I left out was "foot" , or lower unit . A V4 [ motor can be inline or V config] size foot is usually 140 H.P or less with a smaller outside and inside diameter and most 150s come with what we call a V6 "foot" .The prop shaft and diameter is not the same .Different brands use different spline patterns and hardware.Some brands share lower unit sizes . But they might have different gear ratios and horsepowers .Confused yet ? Its one of the reasons that experience counts in the marine biz .
Marc