Prop / Volvo question

[ckspeed]

Hello, first timer here, nice site!

I have a 96 Larson 174SEi, w/Volvo 4.3GS, 190hp, Cobra SX-C1, 1.85 ratio. I'm currently using a 14.25x23 3 blade alum Volvo prop. (stock)

WOT speed is low at about 45mph, RPM is high and past redline unless I back out of it. I've verified tach RPM to witin 100 rpm with an inductive tachometer, and verified speedo within 1-2 mph at speed w/GPS.

Bow rise is terrible, and pulls very poorly on the low end. Top end seems slow for this high a of pitch prop.

Suggestions for prop?? Smart tabs?? Wrong ratio??

Forgot to mention, above informatoin was with 2 adults, empty weight is 1750lbs.

 

[jimmbo]

Re: Prop / Volvo question

Doing the math, 4800 rpm with 10% slip would put the speed at 50.8 mph

 

[Tail_Gunner]

Re: Prop / Volvo question

Stay Tuned

 

[ckspeed]

Re: Prop / Volvo question

Okay, I found a prop calculator online, and it sure looks to me like I should be running a 1.66 or a 1.60 ratio, not a 1.85. With a 23 prop, that would put me at 56 which I would expect, however dropping to a 19 would still give me 46 on the top end or 44 w/15% slip, and I'm assuming a lot better hole shot. Correct? or am I way off base here.

Seems most boats with the 4.3 4 bbl don't have 1.85 ratios, but I've mainly seens mercs.

Ideas???

Thanks in advance for your help.

 

[Tail_Gunner]

Re: Prop / Volvo question

Hello, first timer here, nice site!

I have a 96 Larson 174SEi, w/Volvo 4.3GS, 190hp, Cobra SX-C1, 1.85 ratio. I'm currently using a 14.25x23 3 blade alum Volvo prop. (stock)

WOT speed is low at about 45mph, RPM is high and past redline unless I back out of it. I've verified tach RPM to witin 100 rpm with an inductive tachometer, and verified speedo within 1-2 mph at speed w/GPS.

Bow rise is terrible, and pulls very poorly on the low end. Top end seems slow for this high a of pitch prop.

Suggestions for prop?? Smart tabs?? Wrong ratio??

Forgot to mention, above informatoin was with 2 adults, empty weight is 1750lbs.

Turning a 23 pitch prop @ 4800 rpm show get you about 52 mph, in regards to bow rise it sound's like your not triiming the motor in or out, are you doing that? And yet your over reving at Wot????? Perhap's you have a spun hub, Are you able to check for this, that is where i would start.

 

[Jdeagro]

Re: Prop / Volvo question

ckspeed;

If I read this correctly you are over reving the engine, and the top speed is below what you feel is nomal, and the hole shot is bad. I have been working with Larson (at the factory level) and it appears that going up in pitch whould be better for the top end and keeping the RPMs within the recommended range, however this would only make your hole shot worse.

Assuming everything else is good, you need to change the prop so that you bring the RPM's back down, and install trim tabs to take care of the acceleration and bow rise.

No majic here!

 

[Tail_Gunner]

Re: Prop / Volvo question

ckspeed;

If I read this correctly you are over reving the engine, and the top speed is below what you feel is nomal, and the hole shot is bad. I have been working with Larson (at the factory level) and it appears that going up in pitch whould be better for the top end and keeping the RPMs within the recommended range, however this would only make your hole shot worse.

Assuming everything else is good, you need to change the prop so that you bring the RPM's back down, and install trim tabs to take care of the acceleration and bow rise.

No majic here!

Yes smart tabs will really change how the boat launch's at low speed's and handles well @ high speed's, but i have a similar setup and with a 19 pitch and 1.66 gears i would occasionally hit the 5000 rpm rev limiter and it sound's like he's hitting with a 23 on a 190 hp motor ....dunno there.

Now trying to get on plane with a 23 would be a chore one would think, it certanly would be in a 19" boat, but he's seems to be having trouble on both end's something is not right......

As to prop's looking at his perfromance, a Stilletto Bay Pro 11 in a 22 pitch would seem to resolve a lot of his issue's. It will run noticably smoother than a 3 blade, lift the boat significantly higher out of the water once on plane and some say provide better fuel econ.

A advantge 11 type of 3 blade will run faster maybe 1-2 mph not quite as smooth , but faster. both prop's have a lot of bite and hold a turn quite well. But they come in only a 21p-23p right in the middle.

Running the 22p 4 blade i could only turn it to 4400rpm on a efi motor, dunno here maybe a 1.85 gear ratio will turn that much prop on a 17.5' boat......Still running a 23p and over reving and only what 42mph..... Umm perhap's Walleyedhed or Dhadley will chime in here.