Fresh Water Runabouts

[fasternyou929]

Originally Posted by CasterTroy

Elitist, educated, 2% bastard with your big words, and knowledge n' stuff!

Aw, nobody's ever called me educated before. Swoon...

[Turbo Ghost]

Not knocking on your purchase or anything. Just making a statement.

Unless you are in competition of some sort, I never understood the point of buying a stainless prop for freshwater use. Saltwater will eat one up but, freshwater won't and in lakes and rivers you always run the risk of hitting a log, stump, rock, etc. One good hit with a stainless prop and you've just lost your whole lower unit! (heh-heh...I said "lower unit") An aluminum prop will sacrifice itself and do no damage to the transmission. I've had two instances in the past 20 years where the prop hit rocks when we thought we were in the clear. Both times, the prop folded-up like a tulip and did no other damage. A stainless prop would have probably snapped the output shaft or worse! Just my thoughts on the matter. Carry on.

[Krabill]

A stainless prop will chew through a log with little to no damage to the prop, but will break expensive things if you hit a rock. An aluminum prop will break or bend if you hit a rock, saving the expensive bits.

Lakes with logs = stainless prop

Lakes with rocks = aluminum prop

[Turbo Ghost]

Originally Posted by Krabill

Lakes with logs = stainless prop

Lakes with rocks = aluminum prop

Ours are full of both!

[fasternyou929]

Originally Posted by LeeNetworX

Pitch is how far it will travel forward in one complete rotation, in inches. So I went from 19" to 17", with the objective being to get more spin in a same linear distance, thus providing more thrust powering up from an idle, to ease in pulling a skier/wakeboarder up out of the water faster. Hope I'm explaining it correctly, this stuff is relatively new to me.

Don't know why but this thread randomly popped into my head today. I'm no boating expert (as I'm about to prove), but wouldn't 19" of forward motion per rotation give you a better wholeshot and pop a skier out of the water quicker? I am definitely missing something though, because by that definition a 19" would provide better accelleration AND higher top speed than a 17" rather than a trade-off.

I assume there are some fluid dynamics that come into play similar to HP and Torque, I'm just having trouble visualizing which pitch favors which.

['73 H1 Triple]

Originally Posted by fasternyou929

Don't know why but this thread randomly popped into my head today. I'm no boating expert (as I'm about to prove), but wouldn't 19" of forward motion per rotation give you a better wholeshot and pop a skier out of the water quicker? I am definitely missing something though, because by that definition a 19" would provide better accelleration AND higher top speed than a 17" rather than a trade-off.

I assume there are some fluid dynamics that come into play similar to HP and Torque, I'm just having trouble visualizing which pitch favors which.

A 19" pitch prop will have a slower holeshot versus a 17" pitch. Think of the 19" as highway gears and the 17" as drag gears.

On my 4.3L powered 18' Celebrity, I added a "whale tail" to the lower unit. At the expense of about 2 mph on top end, I get much better hole shots ( made a BIG difference pulling water skiers) and increased stabilty in rough water ( less rocking)

[goof2]

Originally Posted by fasternyou929

Don't know why but this thread randomly popped into my head today. I'm no boating expert (as I'm about to prove), but wouldn't 19" of forward motion per rotation give you a better wholeshot and pop a skier out of the water quicker? I am definitely missing something though, because by that definition a 19" would provide better accelleration AND higher top speed than a 17" rather than a trade-off.

I assume there are some fluid dynamics that come into play similar to HP and Torque, I'm just having trouble visualizing which pitch favors which.

If the engine wasn't fighting against friction and mass you would be right. With those in play the 19" is going to accelerate slower and take longer to get up on plane.

To compare it to something you are more familiar with look at motorcycles. Using the same logic 6th gear (19") would give better acceleration and top speed than 1st (17") since 6th gives more forward motion per rotation than 1st. For essentially the same reasons as a boat accelerating the mass of the bike and overcoming friction means this is not the case.

[Turbo Ghost]

Then of course, you have to walk the fine line between thrust and cavitation! Too shallow a pitch and the prop will rip through the water and not gain any forward traction for the force applied. It's like everything else, it's a trade-off between holeshot and top speed. As previously mentioned, whale-tails make a huge difference in holeshot at the expense of top-end. They also help make slightly smoother wake for wakeboarders and the like.

[shmike]

I understand why a whale tail would reduce top end but how would it help with holeshot? Does it reduce cavitation or a rolling of the boat from torque?

I had a whale tail on my 16'er as a kid but my dad put it on there to reduce the "porpoising" and add stability when the engine was trimmed up at speed.

[Turbo Ghost]

All of the above. It keeps air from being pulled-in from above at take-off and helps keep the drive more level at the same time. They definitely help with porpoising! I had that problem with a Waverunner and put an extended ride-plate on it and cured it right away! For the ski-boat, tabs will also help.