Changed prop pitch and diameter and strange things happened

[89cruisers]

Hello all,

On my 1983 Sear Ray SRV 225 express cruiser with a mercruiser 225 (5.0) I changed my prop and had an odd experience. I was running a quicksilver 15.25 x 15 and my rpms had been only hitting 3700 or so going 31ish mph and hole-shot was poor. since the girlfriend enjoyed wakeboarding on my last faster boat I decided to go with a quicksilver 14 x 13 pitch prop. I threw it on and the engine revs would go up to 4k, but I would only be moving about 12 mph. I quickly returned to land thinking maybe my coupler went bad, threw on the old 15.25 x 15 prop and all is back to how it was. It does appear that the surface area of the fins is less on the 14 x13, would that cause the prop to "slip" since this a 5.0 with a 5k pound boat? I called mercury and they had no idea. I was thinking that maybe either the prop I currently have is to large so maybe I should go with a 13.75 x 15 and see if that corrects things a bit? I have no idea what originally came with the boat, I received the boat without a prop.

 

[NHGuy]

I'd say get a 13 or 14 pitch with a big diameter. There are listings as big as 16x13" and 16x14" in the Michigan Wheel Black Max line. And they supposedly start with 1983. Apparently 82 and earlier were different.

 

[airshot]

Sounds like your new prop is bad...slipping hub...

 

[89cruisers]

The hub is / was firmly in place and the hub came out of the prop just fine (quicksilver props are modular so its just a plastic sleeve) yeah I did see there is a 16 x 13 available, just the 15.25 seems quite but maybe the angle of the 13" pitch blades will fit okay

 

[achris]

Not sure what brand of propeller you are using, but Mercury do a 16"x13" prop, and a 16"x14"... I would give one of those a try... But I do agree, a 22.5' foot boat shuld be a lot better than what you are getting with that 228 engine. another option I would consider is to change the drive ratio. At 13 and 15 inch props you are right down in the low end of the range. If you change the drive top box and have a ratio of 1.84:1 (rather than the current 1.5:1) you will achieve a better boat speed, and use a high pitch propeller. You could change the 13" for a 16"... That will get you back up to the area of props that you have a much larger selection of....

Chris.....

 

[mr300z87]

According to a document on Sea Rays webs site depending one the version of 5.0l you have the original prop was either 15.25 x 15 2brl carb 898 model max rpm 4200 or 14.5 x 17 4brl 228 model max rpm 4600. This was found in owner resource section of Sea Ray's site under parts help. Hope this helps you out.

 

[89cruisers]

Thanks for the correction on the 228 Chris, If I were to keep the boat long term I might consider it, but also thanks to mr300z, I now know know some of those 228 horses have ran away somewhere since my first prop I tried on the boat was a 14.5 x 17 and it was going nowhere. The transom and stringers are solid so there's no extra water weight laying around in there, so I might take some plugs out and check some compression before grabbing a new prop, (engine has less than 700 hours on it so seems odd that something is wrong)

 

[achris]

If you suspect some horses are out of the stable, then a compression test and full tune is where I'd be starting too....

 

[Bondo]

The hub is / was firmly in place and the hub came out of the prop just fine (quicksilver props are modular so its just a plastic sleeve) yeah I did see there is a 16 x 13 available, just the 15.25 seems quite but maybe the angle of the 13" pitch blades will fit okay

Ayuh,.... This prop you put on,..?? Is the barrel of the prop, the same size as the gear case diameter,..?? Or Smaller diameter,..??
If it's smaller, it's an Outboard prop, too small for yer drive,....

Ya might have to go to a smaller gear ratio in the drive, to get the rpms back up,....
Somebody mighta put on the wrong drive ratio,....

 

[MikDee]

The first place I'd look on an older boat, and motor like yours without all the electronics (T.G.) it can have issues with the distributor not advancing due to wear, & tear, & lube drying up. With the engine off, If you take the Distributor cap off, and grab the rotor, gently try to turn it one way or the other, it should move about 1/4 turn one way, then spring back by itself. If not, then take off the breaker plate 2 screws sideways for access to the mechanical advance weights, & springs, check for any broken parts, then clean, & lube. Then put it all together check your point gap, or dwell, first, then set timing, and you're good to go. Next make sure your throttle is opening all the way from the helm to the motor.

It's also a good idea to do a compression test like Chris said, so you know what your working with.

 

[UncleWillie]

Something is seriously amiss.

A 13 pitch prop on a 1.5:1 drive at 4000 rpm and 10% slip is still 30 mph.
12 mph is over 60% slip.
You would have to be Cavitating to do that! (Cavitating, Not Ventilating)

 

[89cruisers]

unfortunately I have the thunderbolt electronic ignition, i would rather have mechanical. The carb is opening up all the way, and dumping plenty of fuel in, the prop on it now (the one ive been running) is proper for the drive (not for outboard) so I have the correct prop. The drive itself appears to be original, I will check the compression later this week or early next week

 

[dubs283]

unfortunately I have the thunderbolt electronic ignition

probably the best ignition system mercruiser ever used, easy to work on, understand, troubleshoot and repair

 

[MikDee]

It appears you're about 1000rpm low at WOT with the 15" pitch prop? I would say there's some serious power loss here. If you have upgraded to electronic ignition my post was useless, but you should verify your timing! IMO, I would also check your spark plugs, & wires, for a dead cylinder, next check your firing order, I've seen, & had engines with 2 crossed wires run smooth all through the rpm range, but never deliver full power. These are important issues, but easy enough to check. Good Luck.

 

[achris]

unfortunately I have the thunderbolt electronic ignition, i would rather have mechanical....

No you wouldn't! Thunderbolt ignition is only one of the best electronic ignition systems around, marine or automotive... Reliable, accurate, simple.

 

[UncleWillie]

Forget the Carburetor and Ignition/Timing Theories.

You are turning 4000 rpm because you are only going 12 mph.
You are lugging under a heavy load.
The fact that you are getting 4K at 12 mph indicates that the engine is running extremely well.
When you get up to 30 it will be closer to 5000 rpm.

A 13 pitch prop turning 4K should easily have you well above 25 unless you are towing another boat.
Something is causing extreme drag.

 

[89cruisers]

I'm just old school and understand mechanical ignition a lot more than electronic (on my wellcraft I removed the electronic ignition the previous owner put on and converted it back to manual and worked great afterwards) My dad had told me once that he once had a car with a 305 in the late 70's that had a "soft camshaft" and from a quick internet search it seems that gm vehicles up until the early 80s had this issue, being that this boat is an 83 i'm starting to get concerned that maybe i'm suffering from this.

 

[UncleWillie]

Forget the Carburetor and Ignition/Timing Theories.
You are turning 4000 rpm because you are only going 12 mph.
You are lugging under a heavy load.
The fact that you are getting 4K at 12 mph indicates that the engine is running extremely well.

When you get up to 30, it will be closer to 5000 rpm.
A 13 pitch prop turning 4K should easily have you well above 25 unless you are towing another boat. Something is causing extreme drag.

 

[MikDee]

I'm just old school and understand mechanical ignition a lot more than electronic (on my wellcraft I removed the electronic ignition the previous owner put on and converted it back to manual and worked great afterwards) My dad had told me once that he once had a car with a 305 in the late 70's that had a "soft camshaft" and from a quick internet search it seems that gm vehicles up until the early 80s had this issue, being that this boat is an 83 i'm starting to get concerned that maybe i'm suffering from this.

Been there, done that, not exactly soft camshafts, I've had a lot of miles on my chevy V8's before, having to do the camshafts. Anyway, just try what was suggested to you, before being a naysayer. Bondo was asking about the prop, because if you had a prop with a hub smaller then the gearcase on there, some exhaust would be escaping over the prop, causing a major prop slip condition. I had a 79'- 20' SeaRay bowrider that would do 50mph fully trimmed out, with a 305/228hp mercruiser 4bbl. with a 14"x19"Black Max alum merc prop You should be in the 40'smph range.

 

[QC]

This one seems like it needs reeling in:

If the boat runs 31 MPH at 3700 RPM with another prop, and this prop runs 4000 RPM and only 12 MPH you have a prop issue. Yes, the engine may be sick as well, but that is a different problem. Yes, there may be some drag, but the larger pitch prop planes her.

1) Get another prop, larger diameter, 13 inch pitch

2) Test

3) Post results

4) Move to next issue on new thread