Prop Question

[Mr. M]

Hello first time poster here.

I recently picked up a 1987 Sea Ray Seville BR 19'. The stock motor was a 175hp but the PO built a newer one with a block from a 2000 ish s10. I have had it out a few time and I think it may have the wrong prop on it which is causing the engine to lug. @ WOT there is a knocking noise around 4000 RPM but if a back it off it seems to go away GPS 35mph (other post indicate possible overpropped). The boat dose have a whale tail on it but symptoms still persist after removal.

Current prop is 48-16318-21. Sea Ray archive states stock is 14x19.

Do you think I am on the right track and if I swapped to a 4 blade would I drop to a 14.5x17?

Typical usage:

Small lake fishing (READ pond:Stupid AZ)
Would like to start water-sports
Normal load 3 people lots of gear/coolers
Occasional 8 person load

 

[steelespike]

Re: Prop Question

Your numbers don't quite add up.Do you know your gear ratio you may find it on the out drive.
Is 4000 your wot rpm? @ 35 mph?
Usually a setup like yours would crowd 50 mph even with the 21" prop.
I believe your wot rpm should be about 4800.using the 21" and a 1.62 ratio 12% slip nets about 50.
a 19" prop about 47.

 

[drewactual]

Re: Prop Question

You've got engine problems, friend...

Did just the block come out of that truck? Or, the entire rotating assembly?

 

[Mr. M]

Re: Prop Question

According to the Sea Ray prop chart gear ratio is 1.84. Engine WOT is 4400-4800. The 35 MPH is around 3800-4000. Noise appears around 4000 and I have not tried to push it past.

 

[Mr. M]

Re: Prop Question

I'm no mechanic but my buddy has pulled the motor to replace a coupler and stated all was well. Boat runs fine except around 4k. I believe it was just the block was from the truck.

 

[drewactual]

Re: Prop Question

Another question: is it a knock, or a harsh tick?

 

[Mr. M]

Re: Prop Question

Kind of sounds more a tick. I have a vid but it is hard to hear.

 

[Mr. M]

Re: Prop Question

TRIM 20130915 151850 - YouTube Here is a link to the video.

 

[drewactual]

Re: Prop Question

I could hear it.. and it sounds like a hydraulic lifter leaking down under throttle... It would be present at all speeds if it were a rocker..

I was worried about the cam if he swapped out an entire rotating assembly, but mebbe he had sense enough to keep a marine cam shaft in there.. a marine cam shaft produces power off idle and throughout the powerband, at the cost of gobs of top end power..

Lifters collapse from time to time.. you can try changing oil to recover it (by using a low weight oil to allow better charge, or heavy oil to maintain charge).. most likely, though, you're going to hafta replace it.. not too bad, but not exactly easy either..

It shouldn't hurt your output TOO much, but left unchecked can and will bend pushrods.


Given your intended purposes for the boat, you may be better off with a 18p than either the 19 or 21... Especially towing for watersports and loaded with eight people.

 

[steelespike]

Re: Prop Question

3800 rpm, 21", 1.84 and 35mph= about 14% slip, pretty normal
Now we need to get a wot rpm and speed.

 

[Mr. M]

Re: Prop Question

Should I run it to WOT even with that noise?

 

[drewactual]

Re: Prop Question

Should I run it to WOT even with that noise?

I wouldn't..

 

[Mr. M]

Re: Prop Question

Ok think I may have found answer to the noise.

Recap:

1987 19' Sea Ray
Merc 4.3l
1.85 geared Alpha one
13-3/4 X 21P prop
Whale tail

Had the boat out today with the engine cover off and the noise appears to come from the water pump (Thoughts?). Decided to take to to wot ~4400 41.9 GPS.

What do you think about running a Hustler 4 blade 17p for towing and full load and a Hustler 4 blade 19p for lighter load?

 

[Mr. M]

Re: Prop Question

Anyone?

 

[steelespike]

Re: Prop Question

I believe the Hustler is available vented,this should help hole shot.A 3 blade19" should put you at around 4700-4800.

 

[Mr. M]

Re: Prop Question

Do you think the vented 3 blade would better suit my usage?

 

[Mr. M]

Re: Prop Question

I went with a Hustler 4 blade 14.5x17. 39MPH @ 4650 RPM

 

[steelespike]

Re: Prop Question

Not sure why you went to a 17 4 blade My suggestion was a vented 19" 3 blade.
An unvented 3 blade 19 should help hole shot and add 250 to 400 rpm.
Venting should further improve hole shot.
If the 4 blade is vented plug the vents.Maybe you can return it.

 

[Mr. M]

Re: Prop Question

Man reason for the 4 blade was for doing water sports/the heavy load. Seems to work well and the RPM were probably a bit higher but I looked towards the end of the run (SMALL LAKE) I also edited the top post...

I may still get a three blade for speed but I am happy with the increased handling from the 4 blade. The whale tail has been removed and I think the older 21p might work better also