motor height pictures transom clamp question

[a70eliminator]

Hi again, I never payed much attention to motor height until now as i just hung the replacement for my piston scored 60hp, I used all the cosmetics from the 60hp including the longshaft leg, cowling ect, an 80hp powerhead now hides behind the 60sportfour cowling and badges.
Do you think the cav. plate is too far below the hull? If I can safely raise it some it would be a good move as I fish alot from this boat and hitting something in shallow water is one of my biggest fears not to mention maybe there would be a performance gain in there too.

Just a side note: I notice alot of play in the motor mount, the top pin of the transom clamps fits loosely into the motor mount and I think thats where the play comes from? Is this normal, that little pin sure has a big job to do especially if I raise to the next notch as the motor will no longer be resting on the top transom cap.
Ok forget all that stuff and go to the last reply which is where I'm at now.

 

[film495]

Re: motor height pictures transom clamp question

I'd certainly test it there before making any changes, my understanding is that about level to the bottom of the transom is default and a little lower will handle better and you will not blow out in turns, but there may be some top end WOT performance loss. Depends how you use the boat, if you want to fly at top speed perfectly straight, you might want to tune that out, but if you like to corner and handle the boat, I've seen 1.5, 2 inches for the Cavitation Plate below the transom. I'd personally test it there and get a feel for it, but if you decide to raise it up, there is a compromise between WOT performance and handling. If you bring it up because you want to have less draft to the bottom, personally I'd want to consider the whole set up as a flats type of rig from the start.

 

[a70eliminator]

Re: motor height pictures transom clamp question

I figured out my loose mount problem, it turns out that the transom clamps aren't fitting flush to the transom, they are held out about 1/8" on the top by transom finish plate, which allows play in the pinch points and the motor to jiggle back and forth. I'll have to grind that 1" or so of the chrome transom plate so the clamps fit flush.

I'll have to pull the clamps off to fix it, and at that time I'll raise the engine 1 notch, it may just save my skeg one day.


In the photos you can see how the transom top plate slightly overhangs the width of the transom causing the loose pinch points, There are two threaded holes in the transom bracket where i could pin it with 1/2" bolts too, so it's either grind some or drill a couple extra holes.

 

[steelespike]

Re: motor height pictures transom clamp question

My motto is raise it to a point just before venting(cavitation) becomes a problem.Just be sure it pumps water.It appears you could gain up to 3 inches.
A tremendous amount.You could gain a couple of mph and a slight improvement in economy.While your prop appears very nice it may not allow max height.Turning Point props deliver stainless performance at aluminum prices.Will help get that ideal height.I also don't know if they are availavble
for your motor.If you can't find a turning point you may be able to have some cup added to your prop.

 

[mars bar]

Re: motor height pictures transom clamp question

Mine sits an 1" above my hull, they say that's ok.

 

[a70eliminator]

Re: motor height pictures transom clamp question

Hi, I've been raising my engine height one hole at a time, I'm now at the third hole and the cav. plate is just slightly below the bottom of the transom, I still have one more hole to raise it which would locate the cav. right even with transom.
Now let me tell you what I have noticed so far, the boat does seem to have a little less bow rise, if I trim the engine out even one step from full in she porpoises, so full in seems to be best, I then switched props from the 10 x 9-1/4 to my spare 10-1/2 x 10 and it looses grip, I put the 10 x 9-1/4 back on and I pulls good from the holeshot to full plane.
At full plane WOT I looked over the transom and I still cannot see the cav. plate, but there is a secondary cav. plate at the leading edge of the extention housing, you can see it in the photo's above, I notice water being flung up and deflecting off of it making a nice fan of spray, I'm just afraid that last hole up may cause this prop to start loosing grip too.
There is a keel that portrudes below the transom, it sticks down about 2" and then tapers up the last 6" to blend in with bottom of the transom, is this something to consider when trying to raise up cav. plate even with transom?
I just realized this may be the wrong catagory for my question.

 

[tashasdaddy]

Re: motor height pictures transom clamp question

it actually looks like you have a long shaft on at 15 inch transom.

 

[a70eliminator]

Re: motor height pictures transom clamp question

It's a 20" transom, the long shaft leg is original to the boat, in fact the powerhead is from another engine which had a short shaft and I had to swap it, just look at the extention and imagine where the prop would be without it, oh wait you already did lol!
I can see what you mean it's almost like a short shaft would work with is adjusted all the way down as it is now, or the long shaft with the adjustments all the way up which is almost where I'm at now.

 

[emdsapmgr]

Re: motor height pictures transom clamp question

Check the engine when running on plane. The water coming from under the transom should hit the lower unit just below the anti ventilation plate. If that plate is (too low) underwater, you will see a lot of water spray- indicating poor fuel economy and top speed. You have no potential for running cupped props on that engine, so a high engine mounting height is not going to help much and can cause the prop to ventilate in the turns.

 

[a70eliminator]

Re: motor height pictures transom clamp question

I don't know if it's the nature of it being a flat bottom or what, but I raised it to the highest hole cav. plate is now even with transom bottom, and now even my good prop sliped like crazy from takeoff, it's ok if i slowly power up but forget pulling a skier, I'm moving it back down and leaving it there, never really noticed much differenece anyhow except running in a little shallower water without hitting bottom. At least now I know this boat engine combo must use a long shaft motor set deep as it was from the very beginning.