Buried Prop on 14 semi-V

Gents,
I have a 14' V, 25Hp Johnson, pin in the 3rd hole. Cav plate is level with the bottom. I'm getting 5,070 RPM with 1-person in the boat and light gear, running a Solas 10-1/8" X 13 prop. The cav plate is under the wash. I tried raising to 4th hole but engine kept blowing out. I'm not going the jack plate route, can I make a starboard shim to fit under the engine clamp without it affecting anything safety wise? Was going to try a 1/2" piece to see it that would make a difference.

Im confused.

Are you referring to the tilt pin?

Im also wondering what a "Starboard shim" is?

Sorry, trim pin, and starboard material to make a shim. Thanks...

What problem are you trying to solve? Is the RPM to high or do you want to trim it out differently?

Sounds like you need less prop to me, a 12 or even 11 pitch.

That is the same prop that I ran on a 60 Merc with a 17' boat.

MrGiggles said:

Sounds like you need less prop to me, a 12 or even 11 pitch.

That is the same prop that I ran on a 60 Merc with a 17' boat.

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Standard prop for that motor and hes well within operating RPM.

As asked above, what are you trying to do here.

3rd tilt pin is possibly why youre blowing out.

Don't know that motor but I'm assuming that "3rd pin" is just about in the middle with lots of adjustment up or down? My outboard has 5 or 6 pin positions. If so, I don't think you need a wedge yet - but I really don't know what you're trying to accomplish.

I''m trying to achieve 5500 RPM because that's what the motor is rated for. I thought the motor height was critical and one of the first things that should be checked. Everything that I've read, says get the cav plate above the water before messing with anything else. If it's below the water flow that it's too deep, causing restriction and drag. What am I missing??

motor height and tilt/trim pin holes would be different things. trimming out to the point you're porpoising means you've trimmed out too much

Raising a motor generally gets you more efficiency and speed, until you get to a point you're too high up. How about posting a pic of your engine height setup, since each boat and engine setup is different. cav plate can usually sit above the bottom. If you're shimming up to test, be sure to put a leash on the motor in case the clamps loosen up. Once you've tested for the best height, bolt the motor up properly.

Good luck! I'd start with an inch and go up from that point.

Thanks, I've made a shim, 10" X 2" X 3/8", from starboard. Will put trim pin in 2nd hole and run with and without the big Polish woman in the boat.

As far as testing, I'll be sure to tighten the clamps. We wouldn't want the engine to fly off :shock:

you're not going to get the cav up, not with that prop.

Solas=cheap.

You will need to look into something that will allow you to run shallower if you want to run it high on the transom; and even then you're going to have to watch the water pressure CLOSELY. You might make a call to Powertech.

The hull has a lot to do with it too. A ton of turbulence back there doesn't help matters any.

Jack plate gets the motor back & up into cleaner water and out of a lot of the turbulence.

If you are level with the bottom you are too LOW (usually).

I recently went through this with a 20 hp Mercury on a 1994 Tracker Pro V16. With just me in the boat I was able to get on plane and run 18.5 mph according to the GPS. With 2 people it would not plane, just pushing a lot of water and about 9 mph. I could hear that the motor was not getting enough RPM at WOT compared to what it sounded like with just me in the boat. First thing I did was buy a knock off Tiny Tac from Amazon so I could see what RPM I was running at. I also bought a couple props from the local classified ads. Price was about the same as buying one new prop. The installed prop was 10 1/8 x 13P. The ones I bought were 9.9 x 11P and 12P. Installed the 11P and took the wife with me to try them out. Long story short, the 11P got me on plane with 2 people in the boat, 18.5 mph and WOT RPM right about 5350 which is right about the top end for a 20 hp. With just me in the boat it was about 21 mph.

The boat and motor are an ongoing project. I have a 25 hp carburetor coming today, ordered it about a month ago. So I’ll be installing that and going back to see how that affects the boat. I now have 4 props, including the original to optimize the WOT RPM.

Prop pitch change is worth about 200 rpm for every inch of change in pitch. Prop diameter change is 500 rpm for every inch. In my case changing to the smaller dia 11P gained me about 600 rpm.

In your case you are one step ahead as you already know what your rpms are were as I was just going by what I could hear initially until I installed the tach. You need to go with a lower pitch prop most likely from your 13P to an 11P. That should get you 400 rpm at WOT 5070 plus 400rpm is real close to the 5500 you are wanting.

I do have a jack plate on the boat and played around with different heights for the motor as well as changing the trim pin position. Those did a little to optimize the boat but for speed at WOT, but didn’t really change the rpm for WOT.

Changing WOT rpm is going to need a prop change, then experiment with motor height and trim to optimize the ride/mph.

Developments:
I added a 1/2" shim under the motor. On 2nd trim hole WOT RPM is 4890. On 3rd hole WOT is 5400 with 2-people in the boat. I think that is the trick. Turbo Todd is correct, if the cav plate is level with the bottom of the boat, it's too low. That might be the correct place for a sail boat or work boat.

I find ‘trim’ can be both critical & touchy in small skiffs and have had many where I needed to move the trim pin based upon if 1 or 2 people in the boat.

DaleH said:

I find ‘trim’ can be both critical & touchy in small skiffs and have had many where I needed to move the trim pin based upon if 1 or 2 people in the boat.

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I think this may be the long and short of it. I'm trying to find a cure-all for fully loaded for fishing, 3-people, 2-people, or just me. The boat is too light and too sensitive to ballast to have a fixed setting. In researching this, I'm finding the southern water-fowl hunting guys are real sensitive to speed. They're regulated to 25HP and they're all big guys with lots of gear, portable duck blinds, and usually a dog. Most have hyd tilt-trim, mounted on a hyd jack plate. Not sure why they're in such a hurry to get out, but all of the forums have motor sections with repairs and mods. They all tweek their motors to get the most speed and they beat the heck out of props hitting stuff.

I had a Richline V which was basically the same dimensions as yours. I had a 18hp and had to raise the motor up 3/4". I used a piece of ply cut to the same width as the transom, then bolted the motor on. I now have a 12' boat with a 9.9 and get the same speed. I have to put the trim pin in the hole closest to the boat with just me and the 3rd hole back with 2 people. I'd say your right in that you'll have to fiddle with it based on occupants. also, have you tried a hydrofoil? I've found they help a lot with small boats like these.

I still get the V-shaped spray coming up from the LU when on plane. The cavitation plate is still under the wash. I think I may shim another 1/2" and try moving the trim pin back to 2-hole and check the results.

keep raising it

as you raise it you will find that you'll have to adjust trim

sometimes you will find that with the motor at a certain height, you won't need as much trim "out".

Also as you raise the motor, you may find that you're over the max rpm. A hundred or two with a light load is fine, but if you're 250+ RPM over, you'll want to go to one more inch of pitch (from 11 to 12 for example).

just went through this with mine. Went with a cmc pt35, raised the engine until it blows out when trimmed to the extent that the boat wants to porpoise. Engine now runs 500+ over max, had to go from 11" to 12", picked up a total of 4 mph. 29 to 33. With my prop and the cmc setback the av plate is up out of the water a good bit. If I trim just right and water conditions are just right, I can hear the prop breaking the surface but it don't take long til it blows out especially with some chop. Could use some cupping but I don't need to run it "that" high-and starve the pump for water.