TOPIC: Grrrrrr!

Over rev with a 19 pitch 2 blade aluminum, do the same with a 22 pitch 2 blade cupped SS prop. ?? Put the 21 pitch 3 blade aluminum on after a very short test with the SS 22, at least I can get to about 5000-5200 at WOT with the 3 blade 21 pitch prop, but mostly with the motor tucked right in to the transom. This video is of the 21 pitch 3 blade aluminum prop starting about 5 grand and bumping up over 5200 as I very slowly trimmed it out. Got to 37 mph.

Smart Tabs shipped today. May wait to put them on before I take the boat out anymore. I'm starting to worry that I'm gonna screw my motor up with all this over-revving, or maybe even detonation I can't hear. This has become very frustrating!

Frank

Frank, I'm still on the bottom of the learning curve, so I certainly won't try to offer any advice here. (I know you're frustrated, I'm hoping and believing with some "help from your friends" here you'll get it all worked out!) I just wondered, what is the WOT tach reading you're looking for, and what kind of speed (MPH) are you hoping for/expecting?

frank, i wonder how many mph is lost by the porpoising.

Thanks for the side views, Frank. Balance looks ideal, not too much stern squat. That cool 2 blade took a step backwards, so the Cat obviously needs blade area. If you can try one, a 22 or 24 pitch Bass Boat style prop with more rake to the blades and mucho cup, or one with four(!) blades would be my next test. Still think something isn't adding up- 100hp, 300 lbs. boat, with tunnels, should go faster with 21" pitch. Had a 14' Checkmate V-bottom with 125hp Evinrude, ski setup, 21 pitch stock OMC aluminum prop, boat weighed 550 lbs. Ran 58 GPS mph at 5700 RPM. I would think your Cat should be in the mid to upper 40mph area.

That video is 5K RPM??? Sounds like mine at 3000ish...that motor barely sounds like its even turning.

You sure you have a good working tach?

Heres mine...about the 19 second mark is roughly 5000.

Let's go in order here... Mark, not really looking for speed, more concerned with the boat working right. High 30's is fast enough for fun, but I know it will go faster, probably into the 40's once I get it working right.

Ron, I figure I'm losing 5-10 mph porpoising.

Kerry, I think yer correct, this boat does NOT like 2 blade props. My prop guy here has a SS 23 pitch he said I could borrow. I need to check that out. I don't want to buy one until I have a better handle on this, and get my Smart Tabs on. Thanks for the suggestions and advice, much appreciated.

JerrfyLube, no, I'm not positive my tach is working, but I'm pretty sure it is. I would like to buy a dedicated outboard tach, but $ has been tight, and I've been avoiding spending another 65-75 bucks.

Frank

i'll be conservative and say i'm losing 5 mph. if that is true then i should be around 40mph if i ever get control of it.

Okay, Frank. Did some research, here goes. 1) 100 hp at 5200 RPM. 2) Merc prop chart says 44-52 mph for 21 pitch aluminum between 4750-5250 RPM. 3) Your GPS top speed of 38 mph tells me you are probably turning around 4000 RPM or so. Conclusions? Your tach is either not set properly, or isn't getting a proper signal. Also, motor isn't making top power. The link 'n sync idea may pay off, but I'll ask the easiest question first. Did you look at the carb butterflies to verify fully open at full throttle when you hooked up the controls? Been burned by that one before, seen it twice since!!!!! I'm surprised by how many don't check this. If OK, timing/throttle linkages may need checking (link and sync) Try the easy things first- I have this feeling its something simple holding things back. Keep us posted.

Personally, i think your tachs not working properly and your over propping it...that motor doesnt sound like its spinning anywhere near 5 grand to my ears.

My 1350 is on a 16 foot, fairly lightweight boat(400ish pounds without the motor) and it struggles to turn a 21P prop...at about 51-5200ish RPM...high 40's, low 50's depending on elevation and water conditions. Your probably similar in size and weight but have a 35HP disadvantage...

A friend of mine has a 1150 on his cat and he runs in the real low 40's with a 19P stainless. I would think a 17-19P(max) would be ideal for your setup.

I agree the motor sounds like it is just cruising along. Sounds nice but not WOT