SS Prop Rpm question

Hi guys I just put a post about a 16p Vengeance I put on my merc 115 4s. It performed well, better than my black max. The one question I have is that when I give it full throttle out of the hole the motor goes all the way up to around 5900 and then settles a little once I am up on plane. It isn't ventilating and the motor isn't revving like the prop is slipping. Is this normal.

Re: SS Prop Rpm question

pokman said:

Hi guys I just put a post about a 16p Vengeance I put on my merc 115 4s. It performed well, better than my black max. The one question I have is that when I give it full throttle out of the hole the motor goes all the way up to around 5900 and then settles a little once I am up on plane. It isn't ventilating and the motor isn't revving like the prop is slipping. Is this normal.

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Is the Vengeance ported....a hole drilled in the barrel just behind and below the leading edge of each blade? If so, yes it is normal. This is why you get the revs rather than the engine lugging when performing the hole shot and results in a much faster shot.

Hole size is related to amount of ventilation which relates to how high the rpm's go and how long it takes for the prop wash to clear out the air. Bigger the hole higher the rpm's and longer it takes.

I deliberately ported the prop on my boat and bored 1/4" holes. Hole shot is much faster and I don't notice that much of an rpm increase but you can tell the engine pulls a lot stronger coming out than it did before. It wanted to load up (bog down) now it doesn't.

HTH,
Mark

Re: SS Prop Rpm question

Texasmark,

It is not ported. Could it just be that because it is a stronger more efficient prop it does this? Again it is not ventilating and I pop right up on plane. Probably is normal just didn't remember it doing this on my black max-probably from the flex in the aluminum.

Re: SS Prop Rpm question

It sounds like the prop is cavitating a bit until the boat gets up some speed. Nothing tragic, but you may want to hold back the throttle a bit until the boat gets up out of the water a little.

Re: SS Prop Rpm question

I took her out again today because I wanted to try them back to back and I must have just thought it jumped higher in the rpm range than it did. Holeshot was great and it built up the rpms good. It actually seems at like 5000 and above it takes a second for it to settle in but never over revs. So overall I think it is just a faster holeshot and probably just over thought it.

Re: SS Prop Rpm question

pokman said:

I took her out again today because I wanted to try them back to back and I must have just thought it jumped higher in the rpm range than it did. Holeshot was great and it built up the rpms good. It actually seems at like 5000 and above it takes a second for it to settle in but never over revs. So overall I think it is just a faster holeshot and probably just over thought it.

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Great. Lots of things to consider on propelling boats. Seems each is an individual case and most folks on here that try to help really agree that the final proof "is in the pudding". Grin.

Mark