Underpropped I think... opinions?

[erikgreen]

Update: I wanted to provide a bit more information to kind of close out this question for the folks that helped me. I haven't really solved the problem yet, but I have a bit more info.

Of course the problem turned out to be a dumb owner

I was loading my boat up for the weekend and I wanted to bring a spare prop along just in case, so I grabbed my old three blade to put in the boat as a spare. The end of the prop at the hub where I've been reading serial numbers up till now is a bit corroded.

But I noticed that there are also numbers including size stamped in the side in one spot. You guessed it... it's not a 19 pitch. It's a 15 pitch prop.

So, my tach numbers are:

5000 rpm at 40 mph using a 15 pitch 3 blade prop
3500 rpm at 40 mph using a 21 pitch 4 blade prop

So reading this I'd say I need a 19 pitch 3 blade or so, or maybe even a 17 pitch 3-4 blade.

I'm glad the mystery is solved, but I can't figure out why a slightly hopped up 350 V8 only wants a 17-19 pitch... I suppose it's just my hull

Erik

----------------------------------

Well, I took my rebuilt Sea Ray SRV-210 out to play this weekend, ran the side scan for a while, and tested the engine.

I was able to get up to about 40 mph on the gps at WOT, which was about 4800-5000 RPM. I'm thinking of changing props - I tested it with a 19p 14.5" aluminum 3 blade that came with the boat.

I think the right prop is probably a 21 pitch 4 blade aluminum. I want to improve my hole shot a little, and 40 mph is probably fast enough, although I will pick up a little speed because of the pitch change I think. Aluminum because I boat in lakes with lots of rocks.

Opinions greatly valued, as always

Boat: Sea Ray SRV-210, 4200 lbs
Engine: 5.7L Rapido Long block w/aggressive cam
mechanical distributor
Rochester Quadrajet with broken choke (got parts for it, just not installed yet)


Erik

 

[TilliamWe]

Re: Underpropped I think... opinions?

You are not underpropped. Or at least not by as much as you think.

Well, if it's an "aggressive" cam, then 4800-5000 rpm is probably right where you need to be. If you go to a 21p 4 blade, you'll probably drop the rpms too low at WOT. An increase in pitch certainly isn't going to improve your holeshot, it'll make it worse.
See if you can borrow a 19p 4 blade aluminum and see how it does.

 

[steelespike]

Re: Underpropped I think... opinions?

I agree if you want hole shot increasing pitch isn't the way to go.
As suggested a 4 blade 19 may help low end performance however it may reduce wot rpm and speed as well.

 

[MikDee]

Re: Underpropped I think... opinions?

Well, here's my 2cents, I had a 79'-20' SeaRay bowrider with a Mercruiser 228hp/305 (5.0) that was a lake boat never bottom painted, I put thru-hull exhuast on it, and ran it in the Great South Bay L.I., it would do 48mph fully trimmed out with a 14X19" alum. 3 blade Merc prop, But it was well past break in, pretty loose (not like yours) I was also running 10-40w synthetic blend oil, and had the idle mixture screws set rich for the highest rpm.

Your boat maybe a bit heavier, But it also has a slightly worked 350/5.7 motor, so it should do better. IMO it should spin a 21' pitch 3 blade prop easily, a 4 blade I don't know? maybe a 19" pitch

 

[erikgreen]

Re: Underpropped I think... opinions?

You are not underpropped. Or at least not by as much as you think.

Well, if it's an "aggressive" cam, then 4800-5000 rpm is probably right where you need to be. If you go to a 21p 4 blade, you'll probably drop the rpms too low at WOT. An increase in pitch certainly isn't going to improve your holeshot, it'll make it worse.
See if you can borrow a 19p 4 blade aluminum and see how it does.

I wish I knew more about the cam, but Raul at Rapido doesn't have a record of what one was installed apparently. That's my only complaint about his service

Since I don't know how the cam affects WOT targets, I was assuming the standard range, 4200-4600rpm. I don't know if the cam would be that different. Raul claims 300hp, but that's all I know about it.

Maybe what I need to do is try a couple diff. props and see what I like best.

 

[MikDee]

Re: Underpropped I think... opinions?

Eric, look at my signatrure link of boats I've owned, there is a 79'- 24' SeaRay Cuddy that according to NADA weighed 4000lbs, with a 17" Merc. Black Max Alum. prop it would do 40mph with a stock 350/260hp. I think your motor has a lot more potential, but maybe your motor needs a little more breaking in, before you can go with a permanent prop? but you really need to know your engines recommended uesful horsepower rpm range.

 

[erikgreen]

Re: Underpropped I think... opinions?

I agree, it should go faster... especially since I spent this winter doing a rebuild of it, all the wet foam is out.

You're right that the motor isn't fully broken in, it's only up to about 8 hours of use so far, which is why I'm not running it at WOT for very long just yet.

I would think that it should at least match the WOT RPM and shaft HP of a mercruiser 260.

One thing I'm worried about is the carb though... it's set with the same settings as it had when it was on the 305 it came from. Plus it's older and maybe a bit dirty/needing adjustment. I wouldn't mind a new carb and intake, but there are other things higher on the list just now.

One other thing - my current sterndrive has no skeg. It broke off completely last summer and I've had problems steering at low speed, so I'm looking into having a new one welded on... could the stub that remains have roiled the water ahead of the prop enough to affect performance?

Erik

 

[erikgreen]

Re: Underpropped I think... opinions?

Well, here's my 2cents, I had a 79'-20' SeaRay bowrider with a Mercruiser 228hp/305 (5.0) that was a lake boat never bottom painted, I put thru-hull exhuast on it, and ran it in the Great South Bay L.I., it would do 48mph fully trimmed out with a 14X19" alum. 3 blade Merc prop, But it was well past break in, pretty loose (not like yours) I was also running 10-40w synthetic blend oil, and had the idle mixture screws set rich for the highest rpm.

Your boat maybe a bit heavier, But it also has a slightly worked 350/5.7 motor, so it should do better. IMO it should spin a 21' pitch 3 blade prop easily, a 4 blade I don't know? maybe a 19" pitch

Hmm... okay, I got some better weight numbers for my boat, and it turns out I'm much lighter than I thought. Right about 3500 lbs total, not counting fuel and two passengers.

So it should do 50+ properly trimmed I would think. Maybe I need to check my idea of properly trimmed.

I'm working on getting the cam info, but other than the prop, what could I possibly check out? It's getting to something close to an appropriate WOT range... could it in any way be making full RPM without otherwise developing power?

Frustrating.

Erik

 

[Tail_Gunner]

Re: Underpropped I think... opinions?

My fellow Minnsotian, befor you do to much more find a way to verify your tach within 50 rpm.....and for the record we need to post pics of our interior's... i am almost done with my nautolex interior (SharkSkin) and having a hell of a time trying to find blond teak to finsih it up...

But i am consistent in some regards... a bay pro11 would seem to be in order here...but tach accuracy is a big thing @ WOT

 

[MikDee]

Re: Underpropped I think... opinions?

In theory, your boat should do about 55! In fact it should have done over 40, with your old 305, did you ever test it? I don't know how you can mistrust a GPS, but I might not trust your tach. You should be able to judge your speed somewhat, 40mph is fast, but 50+mph is a thrill, Oh Boy, the waves are starting to blur! In fact, Maybe your prop is slipping? It's hard to tell, without knowing what rpm your engine is designed for, A 300hp/350 would probably free rev to at least 6 grand, but you might be hitting a rev limiter at 4900/5000rpm? and need the extra prop pitch, or a 4 blade, to bring the rpm in range All I know is, you have a lot of potential, break it in gently.

P.S. According to my calculations, you should have been doing about 50 with that prop, at that rpm?

 

[erikgreen]

Re: Underpropped I think... opinions?

Yeah, it's odd.

I do have a new tach (and a whole new gauge set) that I was planning on putting in a new console when I build one... I'll find a way to rig that up for my next outing in a week or so.

I didn't get a chance to try the 305 at full speed because the block was cracked, although even with that it probably did at least 30, from what I remember.

I dunno... I may have some prop slip I guess. The bottom of the boat has a few patched spots, which are painted over, and I could see a little roughness there costing me a few mph, although it's just a few rough spots... but not 10-15 mph.

I don't think there's any kind of rev limiter.. but I might be hitting some kind of throttle limit.. my throttle lever is messed up, it traverses the whole RPM range in about two inches of travel. 0-2500 rpm is about a half inch, so it's hard to adjust. But maybe I'm not actually getting WOT.

/ponder.

 

[John_S]

Re: Underpropped I think... opinions?

One other thing - my current sterndrive has no skeg. It broke off completely last summer and I've had problems steering at low speed, so I'm looking into having a new one welded on... could the stub that remains have roiled the water ahead of the prop enough to affect performance?
Erik

Erik, it is not worth trying different props until you fix the skeg.

 

[MikDee]

Re: Underpropped I think... opinions?

To figure top speed, I'm gonna use a formula that I got out of an old boating handbook, it has worked well for me over the years! It will get you real close:

4900rpm Divided by 1.5 outdrive gear ratio = 3266 shaft rpm X pitch -1 (18" pitch) = 58.79 mph - 15% (prop slip) = 49.97mph!

Just think, your engine is still tight too, I'd suspect that prop is slipping on it's hub? and I don't think a missing skeg is an issue here, because you don't mention cavitation, or ventilation. Or, your Tach is off

 

[John_S]

Re: Underpropped I think... opinions?

Mikdee,

I did not say the skeg was causing the problem, just that it needs to be fixed before you bother fine tuning a prop. The cart is in front of the horse. Besides that, its probably not the best situation to make high-speed runs without a skeg.

I agree if he has 1.5 ratio drive his current wot mph is much lower than a typical V hull. I doubt the prop is slipping un-noticable at 40mph, and that can be verified easily without a prop change.

Erik needs to:
- Fix the skeg.
- Fix the throttle cable issue and verify that the butterfies are openning fully.
- Verify the rpms.
- Confirm he is using a 1.5 ratio drive. (rotate engine 1.5 revolutions and confirm prop only turn 1 turn)
- Mark the prop to test for hub slipping.
- Retest wot rpm/mph.
- Evaluate results.

 

[erikgreen]

Re: Underpropped I think... opinions?

Mikdee,


Erik needs to:
- Fix the skeg.
- Fix the throttle cable issue and verify that the butterfies are openning fully.
- Verify the rpms.
- Confirm he is using a 1.5 ratio drive. (rotate engine 1.5 revolutions and confirm prop only turn 1 turn)
- Mark the prop to test for hub slipping.
- Retest wot rpm/mph.
- Evaluate results.

Okay, here's what I did:

-Fixed the skeg (welded myself)
-Replaced the throttle with a new Teleflex and adjusted for full throw
-RPMS verified good, at least with a new tach
-1.5 ratio confirmed
-No hub slip
-borrowed a 21p 14.5" 4 blade prop for test

Basically I got the same speed results... 40-41 mph, only now I can't get more than about 3500 rpm... which is too much of a drop for the prop pitch alone to account for.

I think I may need to experiment with trimming the boat... last time on the water I did get one run at half throttle where I got to 30 mph, and it felt like I was skimming the lake, as opposed to most of my other runs which were bouncy and bumpy.

Erik

 

[MikDee]

Re: Underpropped I think... opinions?

Okay, here's what I did:

-Fixed the skeg (welded myself)
-Replaced the throttle with a new Teleflex and adjusted for full throw
-RPMS verified good, at least with a new tach
-1.5 ratio confirmed
-No hub slip
-borrowed a 21p 14.5" 4 blade prop for test

Basically I got the same speed results... 40-41 mph, only now I can't get more than about 3500 rpm... which is too much of a drop for the prop pitch alone to account for.

I think I may need to experiment with trimming the boat... last time on the water I did get one run at half throttle where I got to 30 mph, and it felt like I was skimming the lake, as opposed to most of my other runs which were bouncy and bumpy.

Erik

I don't think trim is the problem, once you're at WOT on plane, it only accounts for about 3-5mph. My 20' SeaRay 228hp/305 would go from 45, to 48mph trimmed out,,, One time with a brand new 14"x19" Black Max Alum prop -50mph

My 24' SeaRay 350/260hp, WOT on plane, would go from 35, to 40mph fully trimmed.

Somethins definitely not right tho?

All my boating back then, was on the Great South Bay L.I., choppy water was an understatement usually.

Ok, I'm gonna go out on a limb here, have you looked down into the carb at WOT, to see if it's opening all the way? If I remember the Qjet correctly, if your choke happens to get hung up at all there is a rod on the left side of the carb, that won't let the secondaries open, EVEN if your throttle goes all thru it's travel! it locks the Secondaries closed while the engine is cold.

Next, is your intial timing setup right? and are you sure your getting full spark advance?

If I didn't know better, I'd assume you have a crossed plug wire somewhere? I've seen these engines run, surprisingly passable, but developing no power.

Also, if I remember correctly, you have the 350/350hp high lift hydraulic Chevy cam in there, it should be cranking some awesome RPM!

 

[MikDee]

Re: Underpropped I think... opinions?

To figure top speed, I'm gonna use a formula that I got out of an old boating handbook, it has worked well for me over the years! It will get you real close:

4900rpm Divided by 1.5 outdrive gear ratio = 3266 shaft rpm X pitch -1 (18" pitch) = 58.79 mph - 15% (prop slip) = 49.97mph!

Just think, your engine is still tight too, I'd suspect that prop is slipping on it's hub? and I don't think a missing skeg is an issue here, because you don't mention cavitation, or ventilation. Or, your Tach is off

I stand by this, as I've been able to get true boat speed this way for years, within 2mph.

If you've got the RPM, is your coupling slipping???

 

[tmh]

Re: Underpropped I think... opinions?

Well, I don't think you can draw conclusions from the two props tested because of a different tach for each. Your rpm loss, as you noted, does not compute. How was the hole shot with the 21" prop? If still OK then maybe the tach is reading low.

I doubt you're going to get 50+ mph with your setup and an aluminum prop. With more hp and higher speeds the SS vs. Alum difference is more significant. 40-41 seems low though, but you are yet to run a prop that seems to get you proper WOT rpm, so who knows.

It's a tough challenge trying to figure out props/engine/performance stuff....lots of variables. good luck! Keep us posted on what you find.

 

[erikgreen]

Re: Underpropped I think... opinions?

Well, the 4 blade prop is a new one, so I don't think that's slipping. The coupler is a possibility, although I'd think once it's spun that it'd just be worthless.

A note on the tachs: For the second test I didn't replace the tach, I put in a spare I had in another hole. They read more or less the same, which leads me to believe that both are good.

I'll check out the carb, I did replace the old mechanical choke on the QJet with an electric divorce choke, and it still may not be working right.

And the engine may still be tight... it's only had about 25-ish hours of use at this point, so not a lot.

I'll be trying it out again this weekend, probably using the 4 blade 21" pitch again before I have to give it back. I'll post back here when I have some more results.

It does steer a heck of a lot better at low speed with the skeg on, which is perfect for my sonar runs.

Erik

 

[MikDee]

Re: Underpropped I think... opinions?

Okay, here's what I did:

-Fixed the skeg (welded myself)
-Replaced the throttle with a new Teleflex and adjusted for full throw
-RPMS verified good, at least with a new tach
-1.5 ratio confirmed
-No hub slip
-borrowed a 21p 14.5" 4 blade prop for test

Basically I got the same speed results... 40-41 mph, only now I can't get more than about 3500 rpm... which is too much of a drop for the prop pitch alone to account for.

I think I may need to experiment with trimming the boat... last time on the water I did get one run at half throttle where I got to 30 mph, and it felt like I was skimming the lake, as opposed to most of my other runs which were bouncy and bumpy.

Erik

Ok, Sorry, I just reread your post, if as you say, you only got 3500rpm out of that prop, which appears to have a good soild non-slipping hub, then apparently irregardless of anything else, your engine is not putting out full power?

Aside from the other items I mentioned to check,

Did you adjust the valves as per the engine builders instructions? Which I happen to agree on. With the engine idling, slowly making each one click by loosening it a bit, then slowly tightening till the clicking stops, (zero lash) then set your pre-load (let's say, at least the stock setting, 1 turn down from zero lash) in 1/4 turn increments, slowly. That is the only true nitty, gritty, way to get it right! It is not that hard to do, just a little bit more inconvenient, but then you know they're done right. I always finish up my valve adjustments that way.

You will notice as you do this, when you loosen them up, your engine will begin to speed up at idle, and get very responsive to the throttle, because it is getting less lift, & duration. Then as you start to tighten them down, the idle will slow down, and it will get a bit lethargic, you may have to raise the idle speed screw some to complete the task of setting the pre-load, don't worry, this is normal, all it means is you're dialing in the correct lift, & duration, for most efficiency, & power through the RPM range.


There's nothing scary, or complicated here, do not be afraid to try it. The worst thats gonna happen is it will get to be a bit messy with oil, by the time you're done, but not as bad as you think! Just be ready to add some oil, usually maybe only 1/2 Qt when you get done. I think if you've never done it, You should, to get a feel of how a camshaft, & engine works, it is a fascinating learning experience!