Need Prop Suggestions, low top end

[stacyt]

Hello Folks

I need some help, I have a 1994 Sea Ray 170 Sig Series, its 16.85 ft long and has the 94 Mercrusier 3.0 with the Alpha one. I am currently running about 35 mph (gps) and according to what i hear, this boat should be a tad faster, close to 40. It has a 14x19P alum. prop #4878120A40 19P, 3 blade prop. I run 4600 rpm at WOT. What should I do for some more top end, I have smart tabs on order and removed the whaletale. I was thinking a four blade 18P. All suggestions are appreciated.

Thanks

Stacy

 

[rndn]

Re: Need Prop Suggestions, low top end

All else being equal, a 4 blade should reduce top end a little.

 

[steelespike]

Re: Need Prop Suggestions, low top end

As stated 4 blade will usually reduce top speed.
Is the prop in excellent shape?Does the motor have good compression and in excellent tune?Are the bottom and lower unit clean.Does the trim work right?
Tabs will help hole shot and handling but not likely to increase speed.
If all these things check out a stainless prop in the same demension may help.

 

[stacyt]

Re: Need Prop Suggestions, low top end

Engine runs like a song, don't have compression readings, trim works great, just changed gimbal bearing and serviced lower unit. All great. So I shouldn't change pitch, just go stainless steel aye?

stacy

 

[Dandelion]

Re: Need Prop Suggestions, low top end

40mph for a 14 year old 17 footer with a 3.0 engine might be a couple mph too much to ask. Having said that, 35 mph is a hair slow, assuming the engine has no issues, you're at sea level, and conditions are calm. You could try a higher pitch prop, like a 21 inch pitch with a slightly smaller diameter, say 13.75 inches, and that would give you another couple mph over the 19 inch prop you have now, however, you'll lose 300-400 rpm's at wide open throttle. Your engine's ideal rpm reading at WOT is 4800, so if you're presently at 4600 rpm's you really don't want to go any lower. At 4600 rpm, with a 19 inch prop in an old 17 footer... making 35 mph is not going to set any records but it's not awful, and it may be the best you can do for all around performance. Be aware that if you go for a higher pitch prop, your hole shot and time to get on plane are going to suffer.

 

[stacyt]

Re: Need Prop Suggestions, low top end

I am thinking its slow. I see other guys in 18 or 19 footers with 3.0's say they get to 40 or 42. I had a 84 glastron 176ssv, with a 115 evinrude outboard that would run 40 mph. I am going to tinker with the air/fuel mixture. I had the Sport 300 fin on the lower unit, which helped it plain alot faster, but I have removed it with smart tabs coming, maybe i can gain a few mph there.

 

[steelespike]

Re: Need Prop Suggestions, low top end

You may want to do a compression check before going to far into changes.
If the motor is original un touched it may have issues.You could just pull the coil wire and ground and just crank it listen for a very even cranking souund
with no surges from a weak cylinder.If nothing obvious go to the compression check.you also could weigh the boat, bare 94 170 bow rider is 1,900 lbs.and 115 hp. If its heavy it may have absorbed water.
My limited research indicates 40 would be really respectable from a 14 year old boat.
With a 4,800 max rpm a change to an 18 or 17 pitch stainless might work.Generally size for size a stainless will produce less rpm than aluminum but more speed.You don't want to lose rpm so carefull size selection will be critical.
Some dealers will let you try props with your intension to buy.

 

[codertimt]

Re: Need Prop Suggestions, low top end

Although I agree with everyone's comments thus far(check condition of prop, boat may have gained weight, compression/power could be a touch down, etc), I really think the boat needs to be tested without the hydrofoil before a real assessment can be made.

My experience with hydrofoils have been that they can really affect the attitude of the boat running down the lake. We all know they keep the bow down during takeoff, but they can also affect bow rise on plane. So if the hydrofoil is not letting the bow come up, then you could be plowing through the water and thus loosing speed.

At 4600 with a 19" prop, you're looking at a prop slip of about 15%. So something is causing drag... The weight of the boat? The condition of the prop? The physical presence of the hydrofoil? How much boat is running in the water because of the hydrofoil? Old prop spinning on the hub slightly?

So lot's of possibilities. I personally thing you're starting in the right place with losing the hydrofoil. And at the very least am quite interested to know what results you get moving to smarttabs. There might not be a full 5mph to be found, but I bet you gain 2-3 at least.

 

[stacyt]

Re: Need Prop Suggestions, low top end

My smart tabs are scheduled to arrive Saturday, so we will go from there. Will also do compression check. Thanks for the suggestions.