Prop question???

[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!

[THEFERMANATOR]

He's now over at bandofboaters on there forum. The old propgods forum is now strictly an archive. His side business is mobile prop testing(don't know his day job). He has a van he loads full of props, and will bring them out for a $95hr charge, and let you test unlimited props. Also if he has a prop you want to test in his test props, he will ship it out to you and let you try it for the cost of shipping and I believe $35. If it works you can buy it, if it doesn't, ship it back and you can try more. It's ALOT cheaper than buying them at full cost, then reselling them if they don't work out. The PERMATRIM did WONDERS for mine, but I still need a better prop to get up on plane better. I ca nactually plant my bow down SOLID at WOT instead of bouncing away, and hold the bow at cruise instead of flopping like a fish on deck. I'm hoping a prop swap, and I can jump on plane, and hold the boat level running without porpoising. When you get done with the boat, he's going to need to know WOT RPM's AND speed as well as ALL the details on your prop so he can figure prop slip and see how it's currently hooking up so he can better judge what prop you will need. Also if you go with a powertech prop, some of them will vary GREATLY in how they hook up. Say you need a 17 pitch in a blade run of the mill OEM type prop. Some of there props will run the same while others will require a 18 pitch, but a few of them hook up so well, you would need to drop down to a 13 or 14 pitch. And engine height is CRITICAL. With my hydragfoil, I actually picked up top end speed, but I have to have the engine height DEAD on perfect before it will pick up and go. A touch to high and it porpoised, to low and it just throws water all over. Gotta love a hydraulic jack plate.

[bradford]

Remember what I said about SOME OTHER CRAP WILL HAPPEN...?

Go to run it to get some wot numbers, jack plate position, etc, and get and overheat alarm leaving Turner Creek.

I'm pretty sure it's a faulty temp sensor or possibly the system check gauge. The pee steam was warm, but not hot, and you can touch the block while running, hot but not blistering hot. Get the same alarm on a cold engine the next day in the driveway.

Just shows how things go for me. LOL.

Thankfully under warranty.

[THEFERMANATOR]

If you want, theres a seller on Ebay selling the diagnostic software and cables. I got mine for my YAMAHA for like $75. It also allows you to check all sensor readings, and check your engine hours broken down into groups.

[garbubba]

I hear you about shims Ferm, but I've had a good bit of experience with high powered skiffs. (We put 200's on out 19 footers, with a jackup plate, they could run through wet mud.)

Often times porpoising is just a trim issue though, a poorly angled transom often, especially in skiffs so that's one place shims will work.

One other thing, is there any weight in the front of the boat? Without some weight up there the only way to stop porpoising is to shove the bow down. The air under the bow will lift it & start the cycle. When my dog wasn't up front, I used to put all the gear I could up there.

[bradford]

Thats what I still need to do, cut some hatches in the rear bulkhead of the casting deck to stow some stuff, plus my dog likes riding up under there too. I think the extra 50-60 lbs an extra foot or two forward is gonna make a lot of difference. When running fast it does feel like she'll blow over if I run her any faster or turn into the wind. Still need a different pitch prop though, and if I'm gonna buy one I want one that the boat performs the way she should under all conditions.

I know what you mean about you La and Miss guys. A friend of mine is a coonass that works on the oil rigs down there.

His dad has a jon boat with twin 115 Mercs on the transom.

[bradford]

Replaced a faulty system check tech and Patrick at Custom Marine let me borrow a 13 x 15 viper prop, the only loaner he had that would fit in the pitch close to what I'm looking for. I knew it wasn't exactly what I needed, but the skiff does seem to ride better. It turns higher rpms and doesn't porpoise as easily, also bumped the jackplate up 2 inches vs 1.5. Gonna finish up the boat before spending any real money prop wise.