Got a new motor, Cavitation plate location???

J

JimG

Well-known member
I managed to find a used 2008 Suzuki V Twin 25hp to replace my Mariner that got destroyed by a vandal. Where should the cavitation plate be in relation to the keel? With the mounting bracket on the transom, the plate is 2" lower than the keel. This is on a 14ft TDB Sea Class.

Jim
 
Where should the cavitation plate be in relation to the keel?
Click to expand...



Hull relation would be what I would be concerned about not the keel. My experience has been flush to 1 or 1.5 inches with the plate above the bottom of the hull.
 
Jim,

Check with the boat and motor manufacturers to see what they recommend for their boats.

I have to disagree with Dave, your cavitation plate should be even with or slightly BELOW the keel to prevent prop ventilation (cavitation). 2" might be a little excessive but not by much. Typically 1" to 1.5" is about right.

This was brought home to me this past October. I was driving a forum members 23 ft. Sea Ark with a 75 hp and couldn't figure out why it was cavitating on a straight line course at just 3/4 throttle. After we got it back on the trailer and put the motor all the way down we could see the reason - the cavitation plate was above the bottom of the hull by about an inch and a half.
 
I agree with even or slightly below. There is a trade off. With the motor lower, she will get up on plane quicker and easier, but you'll loose some top end speed. With the motor higher, it may not jump up on plane as quickly, but will go faster at wide open throttle.

I played around with my 25 HP Merc on my 17 foot tracker Jon. I ended up raising it about 1 1/2 inches, the cavitation plate is about an inch below the bottom of the hull, and I have a good compromise of speed and holshot.

Just my opinion anyways...

Jon
 
I found a 2"x1.5" block of white cedar in my decoy supplies. Puts the cavitation plate 1/2" below the hull centerline and almost lines up with two existing bolt locations. Going to re-drill those holes and utilize the second pair of mounting holes, as at this height, the hand clamps are almost to the top of the transom. The 4 - 3/8" bolts will be carrying the load.
 
I have to disagree with Dave, your cavitation plate should be even with or slightly BELOW the keel to prevent prop ventilation (cavitation).
Click to expand...



Pete,
I can't help that you are an old fart who no longer cares to go as fast as one possibly can. :>) :>) I do get a small bit of cavitation at times but nothing I can't live with. Besides, maybe that extra inch just clears that underwater rock!
 
Last edited:
Guilty on all accounts Dave. I certainly don't have the need for speed "most of the time". As far as that underwater rock - that underwater stump I hit in the dark running WOT that last week of the season would have been hit regardless of that last 2". I was just fortunate that a) I had the motor tilt lever up so it could swing up and b) I didn't rip the lower unit off.
 
Good to read that you found a replacement motor, particularly one that is noted for its reliability. Did the Law ever track-down your vandal?

If you find that you desire a little better tracking on turns, drop the motor back down. The additional hydrostatic pressure on your cavitation plate should improve your this. I would have kept it lower and played with prop pitch.
 
Jim,
I bought a new 25 hp Susuki this year,the dealer wanted to mount it higher than i liked so i opted to mount it myself.

I have only put about 5 hours on it and still have not drilled any holes through the transom.

But the motor manual states "Make sure that when the motor is lowered all the way down ,the anti-cavitation plate is located .o- to 1 inch below the bottom of the boat,"
 
@RLL.... No resolution as to whom the perp is, but it's only a list of 3..... only have to deal with them until my dad passes then don't ever have to see them again.

I run in some places shallow at low tide, so I'd just as well keep the motor as high as possible. Cavitation plate is 1/2" under the lowest part of the hull, and the 1.5" shim puts the bottom mounting holes even with the existing holes in the transom. Not a perfect line up, but close enough that it shouldn't matter once I ream them out to 3/8". Should get me thru the remainder of the season, then when we get warm again, I'll yank the motor and glass in the shim board.

Now to find a tow vehicle. I don't recall if I mentioned, but on 11/23 I had somebody pull out right in front of me and my fiance and totalled my car and she is injured with no improvement to her condition after a month. I just received payment for my car and looking for a compromise vehicle that can be a daily driver/work vehicle during the week and tow the boat on the weekend....only thing I can find in my budget is a GMC Envoy.... Trucks in my price point are pretty spent and don't fill my work vehicle role economically.
 


First trip is Saturday with Mike Rowinsky and his buddy.... We'll see if it will plane. It did with the previous Mariner 2 stroke 25.
 
Jim,
Good luck hunting we have not been seeing much. Ducks are around but in spots you can't hunt. By the time it gets cold the season will be over. I am hoping to go duck hunting on Sat. it all depends on the winds and weather. Maybe I will play golf instead of duck hunting.
Pete
 
I know all about it Pete. The important thing for me is going to just be getting out, and hanging out with Rowinsky for a few hours should be good for some laughs.

And how are the Revicki's doing?
 
Last edited:
Jim,
Things are going good, wife and kids are healthy and doing good and I am in good shape for a fat old man. Work is good and have been getting out in the woods for deer. Didn't carve that much this summer, but have started getting back in the shop and I know Chris has big plans for this winter. You guys are more than welcome to come over and carve if you get time. Say hi to Mike for me and you and your family have a great Christmas.
Pete
 
Sea trial number 1..... we got there and back... 3 guys, 1 dog, and gear. The old Mariner 2 stroke would have had us on plane.... The Suzuki 4 stroke, just pushed us along.... On the lowest transom angle setting, to keep the bow down, we probably did 11 or 12 mph and didn't get us on plane. Went with the second setting on the trip back and dropped to about 9mph. New prop is on order. Went to 4 blades and dropped the pitch from 12 to 11.
 
You must log in or register to reply here.
Back
Top