TOPIC: Video of lower unit running a 23" Al two blade

Wanted to post this video showing the camera pointed at the lower unit when running. Haven't seen too many videos from this perspective.

It looks like I could stand to raise her a little higher, but I'd love to hear what the experts say.

Cav plate is currently 2 3/8" above pad with close to 7" setback on an effectively 17 degree transom. I know Conrad has run much higher without losing H2O pressure with these inlines and that is a good reference. I have a friend who can help me modify my CMC unit to go 1" maybe 2" higher. I do have a water pressure gauge.

Pete

The water coming off the hull appears to be hitting the leading edge of the gearcase at or just below the cav plate. If so, (others should verify or correct) another inch or two is ok. Just keep the pressure gauge in mind while you are grinning from the extra speed. Don't worry- the grin will fade when you realize you need more prop again..... so begins anew the vicious circle for the true speed addict.

I'd try a inch higher. I'll get back with ya on the PM in a bit..

Pete, post that PM ya sent me about the prop grab still I sent ya, as some maybe can learn something. Plus the S+F thread sent about "cup or not". Anyway, My old XS Swit ran 73 with it trimmed out. There was no tilt, just horizontal "race rams" and ran it full full up trim. Surface prop, 14x28 SS 2B cupped and wish I had more pix it. The gearcase was 1/2 out the water and that slapping 2B? REALLY tore up the nose cone end the shaft bearing carrier Even drilled and set screwed in to hold so at least I would not lose the "guts" as M/T cases easy find and not that expensive as compared the price the guts! Went through two before sold..(dumb DUMB move!)
But. heres a pic it. See the taller tail smaller spray, and below that ya can see the thrust off the surfacing blade"? "Props and boats are a WEIRD science, "and I like it!" And Pete? Again thanks as for me sending you that prop? I asked a few bucks for prop and shipping. Pete, your a honest man as...(guys, he's sending me TWICE what I said asked)!

Pix my old Swit

Ya know? Looking at that first pic the "tail"? I wondering if that little spray off top the tail is from the cup in the prop? And as hard to see the real thrust off the slapping blade out the water now. Seeing it real time people on shore said "man ya shove a better Tail than a jet boat, nozzle up!" And NO "squirt boat could get near me either! Had a LOT of fun in that boat, 30 PLUS years ago!

Very good video. And awesome water! Amazed how clear it is.

Im surprised the aluminum prop is hooking up at the height your at. Ive never had good luck with aluminum props in surfacing or trying to go fast.

I do think you can go up at least another inch, but you need to think about a stainless or at least bronze prop .

Doing the math backwards I think your RPM is really low or your slipping the prop a lot.

48mph .09% slip 2-1 gears 23 pitch make only 4850RPM

What is your tach telling you?

Great video!

Conrad

Robby, that is some rooster tail!! It is absolutely amazing that you have these photos (and the stories!)!

I should have my new CMC parts by the end of the week, but then have to gone on a business trip, so won't be testing for a couple of weeks.

PM'd you re:kayakers over on S&F.

Pete

408 michigan super cup 13 1/8th dia 23 pitch. It was made for a 800/850 motor back in the day.
I have one they run pretty good, but not as good as a newer stainless prop. They are super cool looking bronze speed prop to put on a vintage rig.

Hi Conrad,

Yeah, the tach was reading about 5000-5200 rpm in that video. Further trimming increased rpm's but no increase in speed.

For whatever reason, that prop didn't cause very much bouncing to get hooked up - I really like that. That being said, I did replace the rectifier and the system charges the battery nicely now (thanks Doc!), so maybe having a fully charged battery helped to "power through" the bouncing quicker.

I shot the video just to see what's up down there. I really wanted to see what was causing all the spray at mid-range speeds, not sure if that shows up here, but I do like seeing the interaction of the water and motor.

Water out this way is mountain fed, cold and clear. This is a smaller sister lake to a larger one. On the larger lake you can see 20' down it seems - that lake is 700' deep and cold, Lake Crescent. Lake in the video is Lake Sutherland.

Pete

Conrad, thanks for the link. When they say it is cupped, does that mean the prop acts effectively like a 24" or even a 25" prop, in this case?

Pete

Cupping generally adds about an inch of pitch, but its primary benefit is it helps "hold" the water when the prop is exposed to air in a surfacing application like yours.

Its a factory 23 pitch cupped prop. So it should act like 23 pitch. Every prop is different you just have to experiment.

But bottom line you need to step up to better props or your going to be spinning your wheels at this point.

.09 is a good slip percentage number. Your running .16 precent with that aluminum prop. Its like driving on ice and you floor it and go no faster.

Your speed is very good for what props you have right now. Very impressive. You now have to decide if its worth spending more money on possibly only 3-5 mph increase. Or just be happy.

C