prop depth?

[John drawe]

Just picked new boat, Got a 15 hp just to dive it around and get a feel for it.
when i put the engine on the centerline of the prop shaft is 7 inches below the bottom of the boat, is this too deep? Thanks in advance!
John

[fourty-eight N]

get the shaft to be somewhere around 2 inches from the bottom of the boat since your only getting a feel for it. we race at an 1 3/8 below the bottom with the 15hp

[pops67g]

Clarification?

You did not specify if this is a fishing engine you are intending to run or an older long shaft racing unit or what? For racing the prop shaft height can run from zero (even with the bottom) down to an inch and a half deep or so depending on the course and water conditions. Depth is also dictated by rule in some classes.

[John drawe]

Thanks Guys!!!!!!!!!!!!!!!!! I should of been more specific, The motor is a 1974 Sea King short shaft.

[T Chance]

I think you should raise it as high as you can and still keep the water pump in the water. If you get it so high it just winds up and won't get up on plane, drop it down until it works.

By-the-way, nice looking boat!

[pops67g]

The prop is a limiting factor as well

Your Sea King probably has the typical round-eared curly bladed fishing motor prop that was never intended to operate at depths with any part of the blades breaking the surface. I'm fairly sure you will have to build an extension for the top of the transom because "short shaft" on a fishing motor is still quite a bit taller than the shaft length that your boat was designed for. In other words, just adding some shims won't likely be enough. To run right you probably need to set the transom height so that the cavitation plate is even with the boat bottom.

[3autility]

prop depth

Why don't you save your money and buy a Merc KG7H or 20H or KG4H and really go faster than with your Sea King. Even a stock KG7 would give you a better ride! Good luck.

[ZUL8TR]

engine

Why don't you save your money and buy a Merc KG7H or 20H or KG4H and really go faster than with your Sea King. Even a stock KG7 would give you a better ride! Good luck.

Or a Yamato Y80 which can be picked up much less than the good KGxH or 20H (that are hard to find). I run around with a 125 lb Karelsen pickle that was built for the Merc 25ss and it is about the same size as the boat in this discussion. So I use both a 25ss and a Y80 on it.

[PRO-MOTIONRACING]

So that the cavitation plate (horizontal fin thing) is above the bottom of the boat and the water inlet hole(s) are below the bottom of the boat.

[John drawe]

Thanks everyone for the tips and kind words! The Sea King is only for the month of September. I can't wait to take this for a spin! I'll be at Grass Lake as a spectator to check out the different classes.
J.D.

[johnsonm50]

So that the cavitation plate (horizontal fin thing) is above the bottom of the boat and the water inlet hole(s) are below the bottom of the boat.

Agreed, even with the bottom will put the plate in the water as the water rises to seek its own level immediately after exiting the transom bottom. By as far back as the motor is it could be a half to full inch up [to be determined]. Ive done a good amount of fish motor hydro play. A good speed prop fitted to a fishing motor will enhance it nicely but it's not gonna be like a racer. Fun being the game tho it will work well. Good Luck & don't forget you'll be a bit top heavy so smooth manuevering = smooth sailing.

[jeff55v]

When I was a kid back in the 1970-80's, I raced in a small club that required the use of the original service gearcase and tower housing on our motors. We usually took "real" race boats and built up the transoms to fit the motor height. Much like your situation.
What worked great for me was a short 2x4 laid on its edge giving you about 3 1/2" of transom extension ( since 2x4's are not full dimension any more). Then use a couple of pieces of aluminum angle or channel vertically, bolting the board to the boat. Finish it off with a piece of aluminum plate screwed over the whole thing helping to further attach the extension.
As mentioned earlier, you'll want to make the cavitation plate to be on the same horizontal plane as the boat bottom. Maybe slightly lower. Most service props are made to run fully submerged. If your lower unit is too high, your prop will suck air into it, causing it to cavitate.
I hope this helps. Have fun.