Performance question

[ddbyrd3]

Good day all, I recenty bought a 2002 Glastron GX205 with a 5.0 liter V8 and a Volvo Penta SX outdrive.<br /><br />I currently have a 14x21 aluminum prop, when accelerating, it feels as if it isnt biting the water, almost as if it is ventalating. (air around the prop)<br /><br />However, once I get the boat on plane it runs at 4700RPM. I believe it should have a stronger hole shot.<br /><br />I am unsure of the hub condition of the prop, but it doesnt feel as if the hub is slipping (spinning)<br /><br />Would it be worth installing a foil (wing) on the cavitation plate to assure the water remains around the prop? Or does it sound like I may need to change the pitch of my prop?

 

[Don S]

Re: Performance question

Do you use the trim at all? Many boats plane quicker if you start with the trim all or most of the way down, then as speed increases trim up.

 

[Bondo]

Re: Performance question

Would it be worth installing a foil (wing) on the cavitation plate to assure the water remains around the prop?

No.............

 

[Gary H NC]

Re: Performance question

A 21 pitch prop is not the greatest for hole shots.<br />I tried a foil myself and took it right back off..waste of money.<br />Put on smart tabs now all is great!<br />I think if you go with a lower pitch it will help but you would have to be careful with your rpms...i believe 4800 is about max for that engine.

 

[ddbyrd3]

Re: Performance question

Thanks for the replies, yes I trim it all the way down then as I accelerate trim up as the boat planes.<br /><br />Gary/Bondo, why not run the foil? Does it cause too much drag, what are the technical reasons as you see them?

 

[QC]

Re: Performance question

Originally posted by ddbyrd3:<br /> why not run the foil? Does it cause too much drag,

Yes, more stuff in the water is almost always bad. Foils can also introduce some weird and even dangerous handling issues because of the lift that they do in fact provide. One reality check on hydrofoils is why don't Volvo and Merc get in on the action? Why would they let a simple revenue opportunity that apparently has no patent protection get away if it simply bolts up to your product?<br /><br />Back to your original issue . . . I suggest that you spend some time in the prop section. There are no perfect props, but there are those that ventilate less and some that ventilate a little on purpose and those designed for hole shot and those designed for top speed and a lot in between. You are experiencing normal compromise issues; a lot can be manipulated by your right hand and some with your wallet

 

[bruceb58]

Re: Performance question

What is the condition of your propellor? Any nicks or bends? Has it been repaired?<br /><br />When you say that it feels like that the prop is cavitating, what are you observing?<br /><br />Do you have previous experience with similar size boat and motor to know what performance you are expecting?

 

[ddbyrd3]

Re: Performance question

All good questions. <br /><br />QC: I love your comment: You are experiencing normal compromise issues; a lot can be manipulated by your right hand and some with your wallet... Aint that the truth!!!<br /><br />The prop is a "stock" Volvo Penta Aluminum 3 blade. There is NO nicks or bends.<br /><br />I am very familiar with the size and power of this boat thats why I have the concern.<br /><br />However, I have a freind that has a 1998 Galaxie 21' modified V with same outdrive but with a 5.7 liter and he reports the same type of issue.<br /><br />When you drop the hammer out of the hole it feels as if the prop is just spinning with little forward momentum. Backing off of the throttle appears to let the prop take a bite and off I go.<br /><br />No other issues exist except for the hole shot. I am 90% possitive this prop DOES NOT have a rubber hub assembly. It is a casted prop so I can rule out hub slippage.<br /><br />I am contiplating a 14 x 21 4 blade SST Stilleto prop. I would assume this would aid the hole shot...

 

[Mischief Managed]

Re: Performance question

I'd go with a 20" 4 blade. At speed it'll be more like a 21" three blade but it'll offer better holeshot.

 

[ddbyrd3]

Re: Performance question

Thanks Mischief, thats exactly what i am going to do....

 

[ddbyrd3]

Re: Performance question

Well i installed the Stiletto 4 blade 14 x 20 sst prop....<br /><br />Fixed ALL of my reported performance problems!!!!

 

[Bondo]

Re: Performance question

I Always Love a Sucess Story.............

 

[Mile-High Mariner]

Re: Performance question

One reality check on hydrofoils is why don't Volvo and Merc get in on the action? Why would they let a simple revenue opportunity that apparently has no patent protection get away if it simply bolts up to your product?<br />

Merc and Volvo don't "get in on the action" for the same reason that automobiles do not come from the factory with the full complement of power, maneuverability and performance that the aftermarket can pretty easily extract from them: because to do so would subject the manufacturer to increased liability. One less item to warranty, one less item to service and one less item for which to provide a parts supply.<br /><br />And there are patents that protect hydrofoils, at least a few of them. The Stingray(R) is certainly protected by patent, as well as is, I believe, the Doel-Fin.<br /><br />Hydrofoils essentially provide the same benefits as trim tabs, except with some degree of added load (and, therefore, stress) on the outdrive instead of at the hull/transom. Hydrofoils are, like everything else, a compromise; their best contribution comes early in the planing event, at low speeds and with lots of force acting on the rear of the boat. As speed increases and the hull takes over planing function, their effect becomes less contributory and, at high enough speeds, eventually parasitic. Their design is not intended to improve high-speed operation, and so they should not be faulted for slowing you down - only appreciated for their design purpose.