Prop novice with questions...

[Drb007]

I have a 1998 Harris FlotDek 22 foot deck boat. It has a regular wide vhull like a regular boat, not the flat/tri hull like the old Hurricanes. I think it weighs around 3600 lbs. It has a 10 person capacity. It has a Volvo Penta 4.3GS with an SX Cobra outdrive. The only markings I can find on the prop say 14x8x21.
We use this boat for everything. We putt around the lake a lot, occasionally getting up on plane to cool off if it's too hot out. We use it for tubing and skiing.
As it goes right now, it will pop up on plane very quickly with just me and my wife on board. Tops out at right near 50 mph, 5300 rpm. However, if we have the boat fully loaded with 10 people, it takes FOREVER to get up on plane. Once it is up it will top out around 42 mph.
The biggest issue is pulling people up on skis. There is no way it will pull me up (6', 200 lbs) on one ski. It does ok if I'm on two.
I would really like a better hole shot and pulling power. I am fine sacrificing top end (I really don't need to go 50).
I did read a lot on this forum, but don't seem to be able to put an answer together on my own.
Thanks for the advice.

 

[Bondo]

Ayuh,.... The Wot rpms of yer motor is 4800 rpms, yer already under-prop when runnin' a light load,....

Ya might have to stop, 'n swap props when ya wanta ski, or have a full load of people on board,....
Unloadin' the boat of everybody but the driver, 'n spotter is another option when ya wanta ski,...

Yer not gonna find 1 single prop that does everything yer doin' with the boar,....

 

[Drb007]

When we ski it is just the driver and a spotter.

Maybe I need two boats

 

[Sea Rider]

Yep Bondo is quite right. Will need two props for different boating applications to make engine to run towards middle wot rpm range when engine runs at full throttle, although max wot rpm range is preferred in both cases and as loaded for each occasion.

Happy Boating

 

[ahicks]

Somebody that really knows what they are doing might be able to help you out with a little prop magic. Nothing dramatic, but maybe enough difference to get you up on a slalom (not pretty, but maybe possible?). Ask for some ideas, and maybe about cupping options......

 

[Sea Rider]

You can't possibly mix 2 different boating scenarios with such loads difference. Skiing is usually done half fuel tank, skier, spoter and driver and bone dry empty boat.. Can dial a prop just for this occasion to run at max 4800 wot rpm range according to Bondo. Check engine specs to confirm that out. Ideal would be a prop that dials max wot range or even with sligh over revving. Should pull you out with a slalon ski at full throttle. Engine must be 101% healthy to pull you as a rocket idealy on flat calm no wind water cond, say first morning hours.

For second option will need a prop that dials preferably full wot rpm range if will be boating with ten souls and extra load and like running full throttle, be aware that if boating with 3/4 load or less at full throttle engine will over rev, so throttle bit less while checking tach. Assume your tach is in excellent shape and reading order ?

Other costly alternative, check variable pitch props, one single prop for many boating applications. Check Piranha props, they fabricate some nice ones.

Happy Boating

 

[ahicks]

Sorry Sea Rider, but if you ever become involved in this first hand, you may find differently. As mention, no huge differences, but possibly something that will help enough to make a difference. There's nothing cast in stone here. Some prop design attributes aren't really effective until the prop is at speed. The ones we're after will let the prop slip a little (allowing the engine to come up onto it's power curve), and then stop slipping as the boat gains momentum/speed. It's not something you're going to find in a book. It's something you learn on your own, part of becoming one of the few real magicians when it comes to propeller performance....

 

[Sea Rider]

Sorry mate, engine manufactures do not come to an agreement to where the max power curve is achieved. Some states around max wot range, others around middle, so ? Should read different manufacturers tech specs to have a clear clue.

If it were my combo and as a starting point would dial same diam prop with different pitches to make OB to run max wot rpm range for both cases, moving load correctly is all about propping right an engine. If what posted is your personal opinion you should not quote me as if were correcting me about talking out of this world nonsense.

Happy Boating

 

[Bondo]

It's something you learn on your own, part of becoming one of the few real magicians when it comes to propeller performance....

Ayuh,.... I don't dispute what yer sayin' 'bout the black magic of Custom props,.....
But,.....

Ya have to consider the radical load differences of the hull in this thread, Extreme to say the least,....
It's under propped now(light load), 'n still won't pull the (heavy)loads asked of it,....

I've got a small collection of Torque-Shift props,....
11" pitch at idle, up to 26" pitch at Wot,....
I tune it, 'n use it for exactly the opposite conditions Drb007 needs for his conditions, but a change of springs or cams could do the job asked of it,....

'n the market audiences here at iboats, a prop retailer,......

 

[Drb007]

All right boys, everyone to their corner

So if my WOT RPM is too high, I could in theory change props to reduce the rpm, and get even more MPH out of it?

The other variable is that when we get 10 adults on the boat and we are at maximum load, it probably isn't ALL about the prop...the 4.3 might be the limit...the 5.0 might be better?

 

[ahicks]

Yes, I was considering a custom prop. I am deeply indebted to several guys I've met over the years who were absolute magicians when it came to props. I was was quite literally brought up on them as I had performance boats for many years - including a v-drive Sanger that should have killed me on several occasions. These were boats that had very little in the way of manf. specs. We pretty much wrote our own. Today, too old for that stuff - and I don't have the kind of money it takes to go fast any more! Programing/setting up a prop like Bondo describes interesting for sure, but I'll be on the sidelines just watching with interest.

So getting back to the OP's boat, you can't expects something like that to haul 10 people while trying to launch a slalom skier. That's not going to happen. I think one or the other might be possible, but as regarding skiing, the boat in top shape is never going to pull you like a dedicated ski boat that weighs a thousand pounds less.

Not sure what you are using for a slalom ski, but you might have a look around for something bigger to help get you on top a little quicker.

 

[Sea Rider]

Can't possiby go boating with 2 diametrically opposite scenarios with a single prop. If you prop an engine to turm at max wot rpm range for skiing, will surely lug the engine when boating with 10 souls up. Much worse if adding a slalom skier behind the combo. Going for a high tech custom props that meets both requirements can turn into a costly adventure. Check Torque Shift Props or Variable Pitch Ones.

A larger 5.0 Lt engine will move more weight and cancel hull drag faster that a 4.0 one, but will inevitably need to adequate props for top boating scenarios. Will be bored very soon if need to swap props on a constant basis throughout the boating day.

A nice alternative for dual boating scenarios ..

Propulse
https://www.youtube.com/watch?v=dxvsFwqLb-o

Happy Boating