Looking for some Propellor Help

[sraab928]

Hey Guys.... As you may know I picked up a 1992 Grady White Dolphin Last year (Sailfish Hull - Gulfstream Cabin) - With twin 1993 Yamaha 200's - This is a very low hour one owner boat - When I picked it up it had been in storage for about 4-5 years - I had the storage yard do the work and put the boat in the water.

I have been noticing some surging issues when cruising - almost like the motors are fighting each other or something. Also the boat just doesn't seem to perform the way I think it should - Currently gets up to 4800RPM WOT at about 36mph.

I was replacing the fishfinder today (boat is lift kept) - when I was on my other boat working on the new transducer I noticed the numbers on the props - On the starboard motor it says 19-M - On the port Motor it says 17-N and then a letter I cannot read. I am assuming I have a mixed pair of props...

So after all that - I am wondering if any of you have a similiar boat and power combo and could recommend a pair of props that would better suit this boat.

 

[BobP]

There are several prop choices out there.
I have yamaha SW series 17 inch pitch. The RPM approaches 5500, and speed about 45 mph flat out.

 

[sraab928]

I would assume I would need to know diameter and pitch? I dont know what the numbers I found mean? I assume pitch. Maybe diameter is somewhere else.

 

[sraab928]

Anyone else have this combo that can recommend a set of wheels?

 

[Grog]

I don't think the problem is only in the wheels. Is the RPM the same on both engines when flat out? 4800 is too low even for 19 pitch props. I'm running 19's and hit 50+ MPH (1991 Sailfish Yami carb 200's) and the engines could come up 1 hole (the cavatation plate is under while planing). Given the age of the motors I'd rebuild the carbs and maybe replace the fuel pumps, (the plugs and filters are new?). If you go lean too long the engines are toast. Get a good baseline and go from there. If one engine's running 5000 and the other is running 5500 they're missmatched.

What is the load (fuel level, passengers, assorted stuff)?

 

[sraab928]

Ok - I did some runs last night as my surveyor asked some questions. With 3/4 load of fuel... 2 passengers - basic safety equipment. Trimmed out I can get 4900 rpm - both engines WOT - so the props must have been reworked or something as they should be different RPM's based on the markings.

The engines were tuned, new thermostats, poppets, lower units sealed, carbs rebuilt, water pumps etc end of last season. Probably have about 20 hours since then. It should be noted that the speed was the same just after the service as well. The mechanic said and I will quote "she isnt going to win any speed races" - I just assumed thats the way it was with these boats but I keep seeing performance reports on here that are contradictory.

The engines were also compression tested - every cylinder was within 123-126 psi which denotes a strong motor I am told.

I did have a water in fuel problem this year - but have resolved that issue. The motors are running very smooth. They smoke a bit a startup. The only issues I see are low top RPM and a surging feel when cruising. Almost like prop slip and grab. Its not drastic but noticeable. This is my first bracket boat too so maybe some things can be attributed to that.

 

[gw204]

Put a mark on both the drive shaft sleeves and inner hubs on the props. Then run the boat, pull the props back off and see if your marks have moved. If so, you're spinning your hubs and that could give you the surging.

However, I vote for weak fuel pumps.

Also, in my opinion Grady is notorious for mounting the engines on their bracketed boats too low. Check the height of the anti-ventilation plates in relation to the hull bottom just in front of the lower units. For best performance, those plates should be at least 2" higher than the hull bottom (general rule is 1" higher for every 12" of set back). Raising the engines should get you a few hundred more RPM.

My boat originally came with carbed 200s and 14 x 19 SS Yamaha 3-blades. With the 225s that are on there now, I'm spinning 15.25 x 19 Merc Mirage Plus wheels to about 5350 WOT. Ideally, I would like that RPM to be a bit higher, so either 15 x 17 Yamaha wheels or 15.25 x 17 Mirage Plus wheels would be best.

 

[sraab928]

Thanks Brian - I will give that a try - and I will take a measurement and a picture when I put it back up on the lift.

 

[sraab928]

ok - I took the props off and took them to a local propellor shop - He has some computer measuring machine - really great guy... anyway here is where we are at.

The port motor (counter rotater) has the 13 3/4 diam x 17P prop - which measures at 15.6 pitch.

The starboard motor has the 13 3/4 x 19P prop - which had been reworked and now measures 17 pitch.

It appears both props have been modified and are nowhere near matched. What concerns him is that they don't even make a prop that would fix my problem based on the numbers we are seeing. His concern is twofold - first the props need to match - thats a nobrainer but second he feels something is either wrong with the motors or setup. I feel it cant be the motors - as what are the chances that both motors have the same problem at the same time? - Maybe its more the setup.

Im going to take a picture of my motor positions and see what it looks like to you guys. Not there are no props on her but I think you should be able to see - give me a half hour and I will post some pics.

 

[BobP]

Take the sielenserc overs off and verify the throttle bores are fully open with the throttles hammered?, check this with engines off of course.

 

[sraab928]

Will do Bob - just got back up from taking pictures and saw your post - I will have to check that 2morrow.

Here are the pictures....

 

[Grog]

Are the fuel pumps new?

Did your mechanic test the compression or did the sellers? You may want to test the compression yourself (remember to pull the safety cord).

The 15 and change pitch prop should have reved to the moon. Those props seem bastardized, get a new set. Like Brian said the Mercury Mirage pieces are nice. 15.25 x 17's should be good but you're loosing a decent amout of HP somewhere.

Try this: get out and get up on plane and nail it. After about 30 seconds, turn 1 engine off and put it in neutral, and ease of the gas on the running one then pull the plugs on the one you turned off (drop an achor if you have too). They should be nice and tan and if you don't kill the engine fast you will not get a good reading. You'll see righ away of one engine has an off cylinder.

 

[sraab928]

Fuel pumps are original - boat and motors have less than 200 hours on them - but of course that means nothing as they are 15 years old.

I was there for the compression test with my surveyor - He could not get over how clean the boat and motors were.

The props were not there during the inspection - they were stored in the owners garage along with the electronic and factory cushions (still in the wrappers)

 

[Grog]

If the fuel pumps are original, change them (you'll need 4).

 

[G8RDave]

I'm no expert but the motors seem to be rigged way too low. Hard to tell from the pics but the cav plates look like they are lower than the keel and the motors are mounted in the lowest setting. That could explain part of the low revs. If the motors are too low they will be working too hard to push the boat.

 

[sraab928]

They may be low - its hard to tell because you are dealing with the sharp rise of the hull when you look forward. Maybe lifting them a hole would help but I am in no position to be doing that right now with the boat in the water.

 

[plymouthgrady]

PROPS

The engines do look a little low. When running the boat up on plane, look over the transom at the ventilation plates (commonly called cavitation plate) and be sure they are running parallel to the water (you should be able to see both sides). The plates should be level w/ the centerline of the boat so when you're running on plane, just the lower unit bullet and prop are under water.

 

[sraab928]

When I get the props back I will drop her in and try out some of the ideas.

Thanks Guys!

 

[sraab928]

Ok - Got the props back, installed a Garmin 3006 GPS and took her for a run this evening -

Props are now 13 3/4" Diameter - 15.7 Pitch (or cup)

Didn't have a lot of time as it was late - but ran her out - With the tide - Port engine 5000 RPM - Starboard Engine 5300 RPM WOT - 41.8 GPS.... Against the tide - 5000 RPM/ 5200 RPM 37.2 GPS.

I bought new fuel pumps which will go on tomorrow - Then more testing.

I am beginning to think they adjusted the throttles for the mismatched props so it would top out at the same RPM's - as before they were the same - now the props match they are different.....Hmmmm....

As for the engine heights.... here is how they look when running....

Port motor at about 4,300 RPM

Starboard Motor at about 4,300 RPM

 

[G8RDave]

Both are too low with the starboard side being the lower of the two. You should be able to see the cavitation (anticavitation) plate.