TomCat: Permatrims vs 4 bladed prop?

Captain Starbucks

I've done a fair amount of reading on this forum as well as The Hull Truth regarding planning catamarans and the use of foils vs 4 bladed props, or both, or simply recupping my 3 blades. I also had a discussion with Ken Reeves of PropGods. I was surprised to hear Ken tell me that I might actually be better off with Permatrims for my wants, which are simply to reduce planning speed.

I use the boat primarily out in the PNW open Pacific, where the TomCat hull is generally quickly overwhelmed by head seas. I was hoping to lower the minimum planning speed as much as possible. New props are quite spendy, Permatrims are not.

Overall, the boat offers very good performance and I'm happy, but on the days when the going gets tough, I just simply can't fish where I want due to not being able to stay on plane. The "speeding up" option is generally not an option in the ocean. That option I've found works great in chop, but does not work at all in swells, even when tacking-off 20-40 degrees of the head sea. For those unfamiliar with the typical PNW day on the ocean, we get what we like to call "The North-South-East'er" which is a sloppy combination of primary swell, secondary swell and wind chop all going different directions. Oh, then the tide and currents as well.

Engines are 2009 Yamaha F150's. Props are only stamped "19M" and "19ML" on the portside (counterrotater on the port side obvi).

Rob

thataway · Posted: Fri Jul 28, 2023 2:38 pm Post subject:

What is WOT top boat speed & boat speed?

Had Suzukies on TOM CAT & Caracal 4 blade. I had the same issue in chop. Put Permatrims on. dropped the t0p speed top speed by 2 mph. At low planing speed the Permatrim threw up a large amount of water, enough that I was worried about the outboard ingesting water at speeds of 8 to 10 knots. I thought that the Permatrims were a mistake. But the tunnel clearance is an issue.

The single engine is better on the Caracal Cat at lower speed. I have considered adding permatrim & jack plate. However the caracal has better tunnel clearance.

gulfcoast john · Posted: Fri Jul 28, 2023 6:37 pm Post subject:

Rob,

Our TC255 with 2010 Yamaha F150’s came with those same Yamaha 19 pitch painted aluminum props, and we had the same issues in heavy whitecapping slop. At Survey/Sea Trial in flat water in a very light boat they barely got to 5400 RPM (5000-6000 RPM desired). Yamaha makes (contracts out) very good props, but I think they’re overpriced. I’ve had good luck with SOLAS over the years, made in Taiwan.

Solas Amita3 17 pitch four blade aluminum props gave excellent torque and bite around the docks and would get on plane at a lower speed in chop, but at the expense of a WOT RPM closer to 5,000 RPM than 6,000 (higher is better).

Cat O’ Mine is wearing Titan SS 17P props right now. We got 5,800 RPM the other day in ripples even with a very dirty bracket with a crop of half inch barnacles. At ten years I think this one is the best compromise and you get two for less than the cost of filling up with gas.

I just bought a set of aluminum Solas Amita 4 17P (thicker, larger blades for stern lift) for Georgian Bay (all pink granite all around) but haven’t tried them yet. That cruise is on hold due to the 883 wildfires smoking much of Canada.

My Five Star Yamaha tech says we should consider going down to 15P if needed to get over 5500 RPM at WOT when loaded as we most often are loaded. If you cart around 900 pounds of gas on your fishing outings that might be an option.

Go2Marine or LFS marine has a prop finder feature

https://www.go2marine.com/search?keywords=propeller&diameter-fct=14in&engine-make-fct=Yamaha&manufacturer-fct=Solas&number-blades-fct=3,4&pitch-fct=16in,17in&product-type-fct=Propellers&spline-count-fct=15

They have free shipping and 15% off sales.

You can experiment with aluminum props pretty cheap and only lose 2 MPH in top speed (Bob may dicker). Getting your boat dialed in is priceless. A LOT depends on your loading preferences.

PM me for any questions, Hope this is helpful,

John

Moxieabs · Posted: Sun Jul 30, 2023 8:20 am Post subject: Off topic to gulfcoast john

John,
Just returned from 14 day cruise of the North Channel and only experienced 2-3 days of smoke haze, wouldn't let that stop you unless you are quite certain of a future visit to the area. Yes, aluminum props are a better mix with pink granite, don't ask how I know!

thataway · Posted: Sun Jul 30, 2023 9:48 am Post subject:

Switching the engines should give you more stern lift.

Interteresting how fast this thread has gone off subject.

The prime question is how to put and keep a Tom Cat on a plane at lower speed.

Captain Starbucks · Posted: Mon Jul 31, 2023 9:45 am Post subject:

Thank you all for your comments.

Bob, I do not have any recorded data on my boats performance, only top speed, which is 46 mph. RPM at that time was in the mfr's limits I recall, but I do not recall what that rpm was. I never run top speed. I did have a short conversation with Ken at PropGods about engine rotation vs what side they're on. He was stumped on that one. As a former multi-engine instructor, I certainly understand P-factor and the Critical Engine concept in a twin engine airplane, but can't see how that would affect a boat. I'm listening though...

Gulfcoast John, I'm going to shoot you a PM. I'd like to pick your brain a bit more on what you've found. No need for me to reinvent the propeller!

thataway · Posted: Mon Jul 31, 2023 3:30 pm Post subject:

On the boat inward turning props lift the stern, outer turning props depress the stern. There are many similarities in airplanes and the "air" media, but air is compressible, water is essentially not. There used to be a yearly conference:

Captain Starbucks · Posted: Tue Aug 01, 2023 9:41 am Post subject:

Thanks again for the information Bob. I've followed almost every post you've written on the TomCat almost a decade before I actually bought one. I always enjoy reading what you've written here and THT.

I think what I'll do is get a set of props with some serious stern lift for the ocean and save my 19M's for ripping around Puget Sound. Now to just decide between alu and SS for the offshore props. Seems like the F150's are right on the cusp of either making a good choice. You know what it's like in our ocean. If you can make 20 mph, it's a good day! I don't need speed out there. Economy would be nice though. My fishing friends do pay for fuel, but they're not about to pony up $2k for a set of Enertia's!