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Dear Fellow Restorers,

I completed the restoration of my Sea Lancer late last spring. In mid-summer I finally installed an 85HP V-4 Johnson on the transom. The boat has good speed and handling, my problem is when I accelerate, the engine revs high and the prop seems to ventilate until the boat spped catches up with the engine output. The prop is a right hand, three bladed, 13" diameter, 18" pitch unit.

Do I go larger diameter, change the pitch or both?? I think I have more HP than the boat/prop combination are suited for best operation. Your advice and comments are welomed.

Chuck

Chuck, have you tried a different prop ? it sounds like the rubber coushion hub is slipping. This will give the symptoms you describe. One way to check is to remove the prop and mark a reference line across the prop and the inner hub, then retry and check to see if the reference marks have shifted. If it's bad the only fix is an expensive re-hub job at a prop shop or find a different prop ( plentiful on flea-bay)
Joe B

re-reading your post ... another thought ! 18" pitch seems kind'a high for your boat /motor combo, maybe it is just cavitating. I would think a pitch around 11 to 13 would be more apporpriate for your boat. Check for the OEM recommended "normal" application prop size. Too much pitch is not good for your motor as it does not allow the motor to come up to full speed and imposed excessive loading. Of course too little pitch will allow over- revs , not good also. A tachometer is the best way to check, your motor is likley HP rated at 4500 - 4800 rpms , I guessing... check the book to be sure

Joe B

Joe,
Thank you for your comments. I appreciate the help.
Chuck

One day while out with My Seacoaster I was coming out of the hole and all of a sudden the engine reved up but no thrust. I was new to boating so didn't have an idea what it was. I was able to get back to the dock at low speed which I was greatful for. I was on the Illinois River. Anyway it was the Hub. To be sure I put the moter in gear, disconnected the plugs. and gave the prop a twist with my hand and it turned fairly easily. Bad Hub. Anyway it "was" expensive to replace and they found it hard to even know what to replace it with. So I found a site called PROPCO Marine Propellers and got a whole new prop for 60 bucks. I have used it and it seems fine, balenced right and everything. And they had the right size and pitch I was looking for. Johnson doesn't make it anymore. I have a 66 Johnson Super SeaHorse. 40 HP. Thought it might help. Good Luck...Dan

Dan,
My '58 Evinrude is supposed to have a clutch on the prop shaft in case it hits something which will allow the prop to slip rather than breaking the shaft. I always worry when that safety feature might go lame and just let the prop free spin. I'm not looking forward to paddling back. And I don't know if I could change the clutch on the lake.

Verne

Yeah, I don't think I have a clutch. I got a shear pin thats supposed to do the same thing. I got a bag of them just in case on the boat. When I took the prop apart all that rubber hub was destroyed. When I asked my Johnson dealer about it he said a single piece of fishing line could do it and that it would not be a bad idea to check for it periodically. If I realized what happened that day, I could have put the spare prop on and had a good day on the river, and as simple as putting a shear pin on its a different story standing behind the boat than leaning over the transom in waves with a full stomach. I have to hold my breath alot. You bigger guys know what I mean.

Well, I hope I'll never have to do it but if so, I was thinking about paddling to shore and jumping out (if the water isn't too cold). That way I could stand there and work on it. And if I dropped a tool I could retrieve it.

Most all the OMC props have a rubber cushion hub, and I suspect this is also the case with other makes as well. These hubs are designed to absorb the shock from hitting an obstruction without doing damage to the works in the lower unit. All the rubber hub props have some positive mechanical connection between the prop shaft and the INNER DRIVE HUB of the prop. OMC uses a DRIVE pin ( this is not a shear pin), Mercury and others use a splined hub.
The cushion hub is constructed as follows... the rubber cushion is bonded (vulcanized) to the drive hub and this assembly is pressed into the prop hub under great pressure. In normal function any " shock" is taken thru slippage of the rubber relative to the PROP hub. With old age / repeated abuse etc the vulcanized bond may break ... then you have a "slipped" hub that can not be repaired short of replacement of the drive hub / cushion assembly.