Prop slip increase with speed.
 

Has anyone experienced increasing prop slip with increasing speed. I have an '89 Formula 292 with the old blunt nose bravo lowers. I think they switched to the new high speed cases in '90. Either way my prop numbers drop to about 55 MPH which are 11%, then they begin to increase up to 16% at 66-67 mph. I have run both Bravo and Hydro props and both do the same thing. I'm thinking about swapping out the old cases with the newer style. Anyone think that these old blunt cases are increasing my slip numbers?

All of my other boats have always had better slip the faster I go, this is the first time I have experience this.

Yes I know I have posted this also in the Prop section, but I know some guys frequent this area more, so it is double posted.

Are these speeds on GPS or speedometer ? are you over trimming to reach the higher speeds ?

Yes the speeds are GPS. No I am not over trimming. I could not tell you where I am a trim wise, but I know it's not past 8 on the indicators.

Sounds like it could be the lowers. I dont think the original bravo's were meant to see much over 55mph

That's what I think as well... I'm good to 55 mph then the slip begins to really drop. When I look at the guys with 415 hp 502's in the '90 and up 292's they are around 70-71 mph. My engines are putting out all of 415 hp and I cannot get anywhere near those speeds. The only thing I can think of is the drives are at their limit. The boat also feels terrible at WTO, completely not responsive. I've spent hours messing with the the tie bar with little to no improvement.

Endeavour, That does seem high. Does the 292 have the built in hook near the chine at the transom? The 311 doesn't, the others do. Here are my numbers at wide open for reference since my boats are Formulas:

311 23 mirage plus: 8%
272 25 mirage non plus: 11%
206 (single) 23 mirage plus: 16%

Friends 242 23 mirage plus: 13%

how far the drives are down in the water makes a big difference as well...not sure what X dim they used then...

Mine does have hook right in front of the tabs. Prior to this I had a 242 running a Mirage plus 21 and my slip numbers were similar to your friends. Mine was 12.5%. At 69 mph in the 242 so little of the boat was in the water that the hooks didn't touch the water. Now the 292, is much heavier and the hooks are definitely in the water, but I suspect the issue is in the drives or the props.

I've been debating getting new cases or putting nose cones on my old drives. However i have been thinking about adding nose cones for years and it seems that every one that adds them says they are worthless. I don't want to start pi$$ing money away. So I am really leaning towards the newer style cases.

I'm really not sure what the x dimension is on the 292. I know that they are deep. I have measured it before but it was a long time ago and I have now forgot what it was. If I have time today, I'm going to give BBlades a call and see what his take is on this.

Ran one of these over 140 seemed to work fine, may be cheaper than new cases, http://imcomarine.com/cal_store/driv...nose-cone.html I would be looking at the hook in the hull.