Props for Tom Cat

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Doryman

New member
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
 
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
 
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.
 
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.
 
Alok":r7mqqazv said:
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.
Click to expand...

How are you propped, and what RPM are you running at WOT? Do you have a weight figure for your boat in the water?

Warren
 
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
 
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.
 
thataway":26453a8v said:
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.
Click to expand...

I suspect my engines are farther into the water than yours if I recall our previous discussion. My rpms were up to 58/6100 as I mentioned when the engines were higher (though too high initially) I think you mentioned you had a total of 4 bolt holes and yours was on the bottom notch. I suspect the bottom notch on the 2008 engines is farther into the water...

If I were to just trim my engine up farther, would I accomplish pretty close to the same thing?
 
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":2sngnroa said:
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
Click to expand...

Thanks, Marc! Does that mean V4 and V6 as in banks of cylinders arranged in a V?

Warren
 
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.
 
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
 
Doryman":3f1cshht said:
Alok":3f1cshht said:
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.
Click to expand...

How are you propped, and what RPM are you running at WOT? Do you have a weight figure for your boat in the water?

Warren
Click to expand...

Warren: My boat is set up the same way as Dr. Bob's (see his info above). I do not have a weight for the boat.
 
Maybe I am propped OK after all. On the way to Cap Sante I opened her up to WOT and trimmed as best I could. Reached 5700 RPM (did not get that high when trimmed incorrectly before) and 39 MPH. The RPM published range is 5000-6000. Does the fact that I get to 5700 RPM mean I am propped correctly or are there other measurements I should be taking?

Thanks,
Warren
 
I don't know if cats are different, but mechanics say you want to be on the high side of the range, gives some range for higher loads and higher altitudes if needed. Sounds perfect!
 
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