Prop question???

[tsubaki]

Sounds like you been working out of my garage, none of that is new to me.

I just went and looked in the garage, thought I might still have the set we took off the Ashcraft when we swapped the 90 for a 50, but they aren't in there.

[bradford]

Originally Posted by tsubaki

Sounds like you been working out of my garage, none of that is new to me.

I just went and looked in the garage, thought I might still have the set we took off the Ashcraft when we swapped the 90 for a 50, but they aren't in there.

I could have told you ahead of time and saved you the trip, lol

I do appreciate you looking, I have probably give or take 40 props, maybe half in decent to excellent condition, none for this application.




PS, Just for fun I went and counted, I have 38.

[THEFERMANATOR]

You havent seen porpoising till you've rode in mine. And for the record, the only thing shims do is allow more negative trim to make the engine push the bow down more and create MORE drag. Its an awfull band aid fix for a real problem. I still need to run mine again, but I put a permatrim on mine. I want mine to run properly, not with the engine plowing to bury the bow. A properly set up boat should run level with the engine nuetral trimmed or slightly negative trimmed. What happens if you raise the jackplate when its porpoising? Sometimes the engine is mounted to low, and causes it. The powertech scd4 is regarded as the ultimate anti porpoise prop by most, and has worked on quite a few CAROLINA SKIFF'S. It's an easy to tirn semi cleaver design. And the holeshot with them is out of this world. Give Ken at propgods a call, but I bet he reccomends a scd4 in a 17 pitch, and if you buy through him, it's $35 plus shipping to swap props.

[Troutkiller2006]

wish i had prop problems! running the prop that was on the motor on the other boat (mercury vengeance and the last 3 of the model number are 19p, so i guess it a 19pitch?) so far its done a hell of a job out there in the yard, hanging off the trailer. smh

[tsubaki]

FERM, please don't ever go away.
You are a great wealth of information!

[THEFERMANATOR]

I'm on my laptop now so I can type easier. Wedges have uses, but to many people use them as a fix when it's actually a band aid. If you have problems getting on plane because the engines attack/trim angle is to great, then wedges are the fix. But when running, you ideally want your cavitation plate(the one directly above the prop) to be just above the surface of the water, and level with it. Wedges can allow for more negative trim which can plant the bow down and stop porpoising, but it comes at a cost. When you run trim angles like that, you are now using HP to push the boat down instead of forward, you're also pushing your cavitation plate down into the water acting like a water brake forcing the stern up to push teh bow down, but it's still a drag sucking up even more HP costing you more speed, then theres handling issues because now instead of just holding the steering torque of the engine from running, your now fighting 2 different water brakes behind you creating a handling issue making the boat want to fight you when running.

Theres alot to propping, and I won't go into that, but I know flat bottom boats by nature want to porpoise, it's just how they work. If you look at the outer edges of the hull, you'll see all flat bottom skiffs will have some sort of hook built into them. It's like a trim tab, but not angled down very far because they are so long it has more downward push without the short sharp angle of a tab. With heavier 2 strokes and 4 strokes, you stil lrun into problems with flat bottom boats wanting to run on springs though. I've run several stern lifters all designed to stop porpoising, and so far all I have found is I can have it porpoise at different speeds with each one. I broke down and got a PERMATRIM aluminum hydrafoil for mine, but I've used the STINGRAY classic foils in the past with great success. MOST people can go with a prop like the POWERTECH SCD4 which is a semi cleaver design that provides MAX stern lift to plant the bow down without the need of extreme negative trim. They work by refocusing the props thrust more outwards instead of all back which allows the prop thrust to lift the stern up. I know the one I tried got on plane with virtually no bow rise, and made the whole boat feel like it was lifting out of the water.

When I had my 19DLX with the HONDA 75HP on the back, I had really good performance out of the SOLAS AMITA 4 17 pitch. It turned about 5700 RPM's at 37 MPH which I though was pretty good for a 19 foot skiff with a 75 on the back. Only time it porpoised was when I trimmed it REALLY high at WOT, otherwise it just ran NICE. The MAITA 3 ran good to, but didn't have nowhere near the whole shot to it. Now I ran that SAME prop(machined a YAMAHA thrust washer to fit a HONDA/MERCURY prop) on my current skiff, and she bounces at certain speeds. I do know engine height is critical though as you want it as high in the water as possible so it is pushing forward instead of pushing up, but sometimes it's not enough and you have to try some props to get it right. Back to wedges, yes they could be used and probably help, but once you get it set up RIGHT, it will be like a new boat. My JON boat with the little 35HP JOHNSON ran OK, but was a PAIN in the flats, and handled poorly with a 3 blade. Even with the STINGRAY on it, it still was lack luster getting on plane. Put the 4 blade SOLAS on it, and it was liek a new boat. Jumped on plane on the flats, and eliminated most all the steering torque. So once you run one set up correctly, it makes it all worthwhile.

[bradford]

Thanks for the info Ferm, I'm gonna check those out, that site has a ton of info. There's a few things I still have to do to the skiff before she's complete, so before I spend any serious money I want it as close as possible. That guy Ken, is that his business, running a forum and helping people dial in their props? Seems to be highly knowledable about a lot of different boats and setting them up. Thanks again man!