DonCig
07-13-2007, 06:56 AM
I would like to hear from some of you Blackhawk owners on what percetage of prop slip you are you seeing at your top speed runs. I was talking to Brett at BBlades and discussing my recent testing results with him.
It appears after my conversation with him that sometimes with almost all types of prop driven boats the highest speed obtained can be with an induced higher percentage of prop slip (usually by adding trim to the outdrive; more trim than you might normally add).
In my case, by overtrimming the drive and inducing excessive prop slip I gained 4 mph. The risk that ones takes when doing this is first you need enough rpm room with the engine prop combination to allow it; so if you are already on the prop limiter than you probably can not tell if this applies to you. You also need to make sure that the boat can still carry the bow; or else you will get a high speed porpise or an instant bow steering condition; both leading to some tense moments.
I talked to Gerometto and he has seen the same results on his boat; 16% slip to 19% slip yields his top mph in a slightly overtrimmed position.
In my case I saw my top speed increase when going from what felt right to an actual 17% slip.
In my case my Blackhawk drive is most effecient at a 12% slip rate; but this setting is not necessarily the fastest scenario.
Here is a link to a prop slip online calculator to assist you in posting your results.
http://www.go-fast.com/Prop_Slip_Calculator.htm
Thanks!
It appears after my conversation with him that sometimes with almost all types of prop driven boats the highest speed obtained can be with an induced higher percentage of prop slip (usually by adding trim to the outdrive; more trim than you might normally add).
In my case, by overtrimming the drive and inducing excessive prop slip I gained 4 mph. The risk that ones takes when doing this is first you need enough rpm room with the engine prop combination to allow it; so if you are already on the prop limiter than you probably can not tell if this applies to you. You also need to make sure that the boat can still carry the bow; or else you will get a high speed porpise or an instant bow steering condition; both leading to some tense moments.
I talked to Gerometto and he has seen the same results on his boat; 16% slip to 19% slip yields his top mph in a slightly overtrimmed position.
In my case I saw my top speed increase when going from what felt right to an actual 17% slip.
In my case my Blackhawk drive is most effecient at a 12% slip rate; but this setting is not necessarily the fastest scenario.
Here is a link to a prop slip online calculator to assist you in posting your results.
http://www.go-fast.com/Prop_Slip_Calculator.htm
Thanks!