speed loss from a 24p to 26p?

[jperki00]

I have a 1992 bayliner 2052, i was running a 24p mercury rampage SS prop and the 1.47 gears in the upper. Anyway at 5100-5200RPM WOT i was able to hit 55mph GPS. well we wanted to get our RPM range down to the 4600-4800RPM WOT so we upgraded to a 26p mercury tempest plus, but in fact our rpm range went up to around 5400-5500 RPM WOT and we went down to 51MPH GPS.

what the heck could be causing this and why?

NOTE: we already played with the PVS plugs, prop came with "large" vents, we bought the "small" plugs and the fully capped plugs with very little to no change, maybe due to thru-hulls?

 

[steelespike]

Re: speed loss from a 24p to 26p?

It is usually recommended to stay with the same brand,model and material when changing props.
It appears the Tempest is not suited for your application.Unfortunately I can't help with a detailed explanation.But from a very brief search it does appear the Rampage is associated more with high performance.
While it is a bit of a comprimise you could have a good prop shop add a little cup or pitch to your rampage.

 

[jperki00]

Re: speed loss from a 24p to 26p?

thanks for the reply, have any idea what props people are running on the 21ft bajas and scarabs and performance boat?

 

[steelespike]

Re: speed loss from a 24p to 26p?

You might go the the scream and fly site.As I understand it they are fiddling with speed all the time.

 

[not enuf toys]

Re: speed loss from a 24p to 26p?

Sounds like you are having an issue with your tach.

What motor?

I'm a 96 21 ft with a 5.7 lx on alpha 1 gen 2 with the same gears and was having a tach issue this year from bad battery terminals. Started this year showing 5200 at 57 mph with a 21 pitch which seemed wrong. Once fixed the tach shows 4300 4400 thus I am looking and going down in pitch.

 

[Tail_Gunner]

Re: speed loss from a 24p to 26p?

I have a 1992 bayliner 2052, i was running a 24p mercury rampage SS prop and the 1.47 gears in the upper. Anyway at 5100-5200RPM WOT i was able to hit 55mph GPS. well we wanted to get our RPM range down to the 4600-4800RPM WOT so we upgraded to a 26p mercury tempest plus, but in fact our rpm range went up to around 5400-5500 RPM WOT and we went down to 51MPH GPS.

what the heck could be causing this and why?

NOTE: we already played with the PVS plugs, prop came with "large" vents, we bought the "small" plugs and the fully capped plugs with very little to no change, maybe due to thru-hulls?

Lets start over: 1.47 gearing 24p prop 5100rpm @ 55mph....Tach is bad

Heres a base 1.47 @ 5100 W/24p nets a thero speed of 79 mph actual 55mph nets 30% slip

Common slip is 12% that nets 70 mph...Unless you have a 500hp motor in the boat you tach is probably the problem here.

 

[jperki00]

Re: speed loss from a 24p to 26p?

Sounds like you are having an issue with your tach.

What motor?

I'm a 96 21 ft with a 5.7 lx on alpha 1 gen 2 with the same gears and was having a tach issue this year from bad battery terminals. Started this year showing 5200 at 57 mph with a 21 pitch which seemed wrong. Once fixed the tach shows 4300 4400 thus I am looking and going down in pitch.

ok we took out the 305 and swapped to a 355, gasket matched ported and polished heads, split cam running max duration without water reversion, stock mercruiser exhaust manifolds to 4" SS thru hull tips. intake manifold is a high rise with 4 barrell 650 CFM holley...

we should be at around 375HP

and before you say anything about being alpha one gen 2, we are running a drive shower and change gear lube regularly, seems to take it fine since were easy out of the pocket

 

[not enuf toys]

Re: speed loss from a 24p to 26p?

Seems like a lot of work to only be 55 mph....

 

[funk6294]

Re: speed loss from a 24p to 26p?

I am thinking something doesnt sound right. If you are running that much prop and rpm and only seeing 55 you have a TON of slip. Being that it is only a 21 foot boat I wouldnt expect the 44 percent slip that you are seeing with the 26 pitch prop (in theory with no slip you should be around 91 mph with your current combo). Unless you are running the boat with the trailer still attached something is up. Either your tach is off, the gears are not what you think, or the props are mis labeled. Any way you look at it, something doesnt add up.

 

[jperki00]

Re: speed loss from a 24p to 26p?

Seems like a lot of work to only be 55 mph....

your telling me man, we were shooting for 70 MPH but after we GPS'd 55 with the 24p we figured 60-63 with a 26p or 27p would be possible but we want to maintain decent plane. im going to take both props to my local prop shop and get them checked out as far as cupping, and get the hub checked as well, becuase they were ebay specials, thats all i can do, i also know that ive got alot of drag due to this "rhino lining" type lining on the bottom of the hull. this boat used to be salt water and they put this coating on there that i think may free up a few MPH if i get it off. the motor was tuned and jetted by our local performance shop so i know its all there..anything else that could be causing this? ive dumped alot of $ into this and i wanna see it to its full potential.

 

[funk6294]

Re: speed loss from a 24p to 26p?

I am interested in your bottom paint situation. Is is just bottom paint, or did someone actually rhino line it? A dirty bottom will certainly cause some loses (i would imageing actual rhino lining would be very signifigant), but just having bottom paint should not really cause a lot of loses, and if it was dragging really badly i would think you would have problems pulling to RPM. Post up some pictures of this bottom paint set up I am curious as to what was used and how rough it is (really rough like a truck bed, or orange pealed like a roller painted wall). Also, if you have an alternate tach that you can wire up as well, double check that your current tach is not off.

 

[jperki00]

Re: speed loss from a 24p to 26p?

I am interested in your bottom paint situation. Is is just bottom paint, or did someone actually rhino line it? A dirty bottom will certainly cause some loses (i would imageing actual rhino lining would be very signifigant), but just having bottom paint should not really cause a lot of loses, and if it was dragging really badly i would think you would have problems pulling to RPM. Post up some pictures of this bottom paint set up I am curious as to what was used and how rough it is (really rough like a truck bed, or orange pealed like a roller painted wall). Also, if you have an alternate tach that you can wire up as well, double check that your current tach is not off.

these are iphone pictures so bare with me

bottom at a wierd angle

gel coat to rough schtuff transition

different view to see texture

the magical floating boat, i guess were gonna start sanding


what do you think funk, pretty gnarly eh?

 

[funk6294]

Re: speed loss from a 24p to 26p?

Pretty hanious for sure. Sanding or stripping would be a good start. It was hard to tell for sure but it looked like someone seriously did use truck bed liner. Also it looks like it may not have adhered all that well either. Before you start sanding try to see if it will peal easily. What i am about to suggest is not without some risk, but has been done by some to strip corvettes. If it is a thick bed liner stuff try using a razor blade at a close angle to the hull and see if you can peel the coating off. Be forewarned though that it can lead to the need for some gel coat repairs.