suzukidave
Petty Officer 1st Class
- Joined
- Jul 1, 2000
- Messages
- 387
Hi out there, I'd be interested in any advice I can get on propping my boat. My problem is no tach and not much feel for what is "right" performance when you switch to a larger pitch. A prop shop sold me a higher pitch prop they had in stock "on approval" to try and the performance is so totally different I'm not sure what to make of it, but I think I've gone from being underpropped to overpropped. What I want is a good cruising prop with a higher cruising speed and economy being the priorities. I'm thinking of putting smart tabs on the boat to go with the new prop but I'd like advice on whether this will reduce the new and different problems I have, and also whether the new problems are a sign I should return the new prop (which I can only do within the next 2 weeks).<br /><br />The boat is a 16 foot 1000lb deep v fiberglass fishing runabout with a suzuki dt55m motor. The prop that came with the boat when I bought it is 11.5 diam x 11 pitch aluminum. It leaps on plane instantly no matter how many people you put in the boat. It runs out to 25-27 mph at w-o-t and handles beautifully, but it's very noisy, especially over 20 mph and it just sucks gas at over 22mph. I worked out that the theoretical top speed for that prop at 5500 rpm (max revs) is 29.88 mph without allowing for slip, so that means if it was running at 25-27 mph at w-o-t rpm (no tach so I don't know) it would be 14% slip or better, which sounds too good for a boat that isn't just built for speed. Based on that, the noise and the planing perforamce I figured I was underpropped. I want to save gas and cruise faster.<br /><br />So the prop shop let me try an 11 diam x 15 pitch stainless steel general purpose prop (the only thing in the ballpark they had in stock). It's a whole different boat but not all good. The throttle is less responsive. It goes on plane in about 5 seconds, and with a full load of three guys and 2 kids more like 8 seconds. I calculate the theoretical w-o-t top speed without slip would be 40.75 mph. In practice it topped out at 31 mph so that's 24% slip if it's at full w-o-t (which I doubt). It's way way way quieter at every speed. It doesn't sound like it's straining, although revs are definitely lower. However, it does some things which my boat never did with the old prop and I'm not sure if these are things that just happen when you prop a boat more for speed or not. Number one, it had trouble holding onto 31 mph in a small chop and wanted to slip back to 27mph (my old prop runs steady at any speed in any water). Number 2, with a full load the new prop was 2 to 4 mph slower (my old prop runs the same speed with any load). Number 3, when hitting a wave the new prop seems to hesitate and lose rpm in a way the old prop never did. Number 4, the boat trims with the bow a little higher, especially at lower speeds, and the steering and handling is sloppier, plus it's much easier to fall right off plane if I slow down for a wake or something.<br /><br />Is this just what you get if youn increase prop size? I'm thinking of trying this new prop with smart tabs but I'm worried that if I'm overpropped I'm hurting the motor. <br /><br />thanks for any suggestions!