Stern-lift prop vs Permatrim vs Bigger Tabs?

D

Darkwater

New member
Hi. I am looking to improve the mid-range performance of my new-to-me 2008 22 Cruiser.

Specs: Honda BF90D (60 hr), and also Yamaha F6 kicker which adds 60 lbs to the transom. Has Bennett trim tabs 12" wide (across the transom) x 8" deep (fore-aft) (I don't see this size in Bennett's current catalog). 13.5" x 15" 3 blade original Honda prop.

Performance: Boat not heavily loaded (200 lb fuel and water, 200 lb gear, and 180 lb skipper, 1925 lb hull and 425 lbs of motors -- total about 3000 lb.) Top speed (in 1' chop) 20 knots at 5500 rpm. The top surface of the motor ventilation plate, when trimmed parallel to the boat bottom, is about 7/8" below the bottom of the transom. There is a hole available to raise the motor 3/4".

I can't seem to get the boat "happy" in the 13 - 18 knot range in a light chop, after trying various combinations of trim tabs and engine trim. On plane, the boat seems to want trim tabs at 100%--or more. At 18 knots it pounds too much, and when I slow to about 15 knots, the boat slowly drops off plane. My Bennetts are smaller than the M120's which many feel are ideal for a 22.

This forum heavily favors Permatrims to improve mid range characteristics. However, before drinking the Permatrim Kool-Aid and drilling holes in my motor, should I try a new prop? I have seen some props advertised as "stern-lift" e.g. Solas Amita 4 and HRTitan 4. I am wondering if anyone has found good mid-range improvements with a "stern-lift" prop?

Should my Bennett tabs be converted to M120's?

I would much appreciate any experiences and what specific models of prop helped or did not help. Did you raise the motor in combination with the 4 blade "stern-lift" prop? Thanks much! (There is no "prop shop" anywhere near me!)
 
The Permatrim is the cheapest of the Kool Aid in terms of probable positive effects IMHO. I would think raising up the motor the 3/4 of an inch would get my vote also. As for a prop I would have to defer those questions to someone with your combination. I can speak for the Permatrim as it seems to increase low speed maneuvering and we only use our trim tabs in a cross winds to level the boat as we slide loads and manage the fuel tanks levels to level the boat side to side in normal conditions. Larger trim tabs for me would be the last choice; for me a least.
D.D.
 
I second the Permatrims. Not only in control ability, but ours do extra duty as a reentry platorm for people and dogs without having to deploy the ladder or dog ramp. Our canines have learned to go to the port motor which I keep slightly turned to starboard so they get all four paws on the Permatrim and just hop right onto the dive platform. Makes a good seat for enjoying the water while we have margaritas or whatnot as well.
 
I didn't drink the cool aid but got a boat that has permatrim 115 mercury 4 strk 15 pitch 3 blade prop. In a word "awesome". My last 22 had trim tabs (side to side) only 90 yammie 15 pitch 3 blade prop. It really needed the permatrim.
 
We started with trim tabs and found they had to be way down to bring our heavily loaded 22's bow down. That meant they created a lot of drag so we had to trade off between bow up higher speed and bow down, drag, lower speed more gas. Went to Permatrims. Very happy. They control the fore and aft trim easily, we now use the trim tabs for lateral trim. We are Permatrim believers.
 
m2cw

Raise the OB up a notch (not sure which hole it is now, if has 4 holes then the top hole is #1 and bottom hole closest to water is #4) , sea trial then re evaluate other options
 
Another possible clue: Along the forward base of each blade of the prop, there is a line of pits which I assume are due to cavitation. There is a photo of this in my album.
 
Good Advice so far:

1. Add the Permatrim (best easy fix).

2. Raise the motor (You're dragging the lower unit.) Also cheapest!

3. Extend your existing trim tabs to get more surface area and better leverage. (A bit more work, but also very effective, since yours appear to be too small.)

email or PM 3rd Byte, and he can direct you to the story/thread and photos of that exact project which he has done.

4. Look at your boat and consider whether it's too stern heavy and moving some weight forward would improve the performance in chop without excess trim on the trim tabs and motor (inc. Permatrim).

5. Do the above, then check your performance and decide whether your existing prop is performing within expectations.

Good Luck!

Joe. :teeth :thup
 
I can't speak to the pits on the prop, as that is outside my knowledge. However, from reading and talking to various folks, I get the idea that often engines are mounted a bit too low. This is because if they are too high customers will come back and need tweaks; whereas too low can be lived with. So it's "safer" to mount them a bit low.

There is a thread in the archives where I was asking about various props/WOT/etc. for my boat, and someone linked me to a discussion on another forum showing how the leg of the engine/Permatrim/anti-ventilation plate is supposed to look when at speed. An identical photo of my engine shows that it is too low in the water at speed as compared to the best position. I plan to raise it to the top notch (will be around 1.5" higher than now) and test that.

Another 22 owner did just that, described here (handy for me, it is the same engine/dealer who did mine, which is at the same height). Figured you might be interested to read it.

http://www.c-brats.com/viewtopic.php?t= ... highlight=

Sunbeam

Edited to add: Here is a link to the posts on engine height that I mentioned above:

http://www.veradoclub.com/smf/index.php?topic=137.0

The photo from that article showing "too low":
toolow-1.jpg


My engine (hmm, looks very similar!):
IMG_1985.jpg

The photo from the article showing "just right":
correctheightVSmall.jpg
 
The anti ventilation plates on our motors are at the same height as the bottom of the hull. On plane they are under water.
I raised them one hole to get them out from under water while underway hoping for increased efficiency and perhaps a bit of bow down attitude.
The hoped for benefits were not significant but the prop ventilated with a small amount of upward trim and vibrated with down trim.
You should be safe with the AV plate at the height of the hull bottom. Depending on where the motor mount holes were drilled a you may be able to raise the motor a bit above that.
 
is 5500 rpm WOT?

If you raise the OB then re check WOT. I thought this OB is a 6000 rpm and made for it. You should get as close to the limit as possiblle, if not you are lugging the engine

m2cw
engine height first
acheive max rpm second
third add ons, props (3 or 4 blade), etc

Just so I know, are the tabs fully operational when running?
 
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