Help with prop hub spun issues

[Pessemist]

OK guys, no one seems to be able to figure this one out.

Last year I bought a 1988 Searay Sundancer with a 7.4L Mercruiser and Alpha one stern drive.

Every second time I took it out last year the prop hub would spin. We did not hit anything and we were running the throttle in the river like a pampered baby. The prop would just make a clunk noise and then free-spin.

After two prop hub changes and then a new prop it did it again. At that point I had the yard tear her down. We found that the stern drive had a twisted driveshaft. Not wanting to chance a repair I bought a new aftermarket stern drive.

The original Alpha 1 sterndrive had a 1.32 gear ratio but the after market stern drive has the 1.47 ratio for the top gears in the unit (best I could get)

With the new unit I thought my prop spinning troubles were behind me but after about 25 hours (10 being careful break-in hours) the prop spun again in the middle of the river. Again, we did not hit anything.

The sterndrive unit DOES have a Dolphin wing installed on it to which a Sterndrive shower is attached

The original Searay prop spec for this boat was 15.25x15"

I am currently running a 16.25x16" prop which actually allows me to hit about 4600rpm's which is over-reving the 7.4L engine rated at 4500rpms (I do not do this. Almost always cruise at 3800-4200rpms)

I thought about going up in pitch a step but figured that would put MORE strain on the prop hub. Although I would like a prop that allows me to plane around 3400-3600 rpms which I can't really do now.


The boat is now docked at a marina until Monday when a mechanic can look at it. This is getting really expensive really fast. If I don'6t get a clue soon I will put anew prop hub on it and sell it quick! Otherwise I love the boat but I am tired of being stranded.

Thanks for any help you guys can throw my way!

 

[Maclin]

Re: Help with prop hub spun issues

Are the props all the same brand and type? If so seems like a mis-match of prop hardware (thrust washers, nuts, etc...) could be a factor.

Is all prop "furniture" replaced with the prop hub change?

 

[Pessemist]

Re: Help with prop hub spun issues

Are the props all the same brand and type? If so seems like a mis-match of prop hardware (thrust washers, nuts, etc...) could be a factor.

Is all prop "furniture" replaced with the prop hub change?

The first prop was a stainless. The second was aluminum. Not sure of brand. First couple of changes used plastic prop hub and stuff that came with it. Reused thrust bearing. New nut. With new stern drive the yard installed prop. I would hope they used new thrust bearing but not sure.

The second prop which just failed used a hard rubber hub.

 

[alldodge]

Re: Help with prop hub spun issues

Last year I bought a 1988 Searay Sundancer with a 7.4L Mercruiser and Alpha one stern drive.

!

I would say you have to much engine for the prop. If this was a Bravo drive the prop hubs are made to handle more HP and torque. The 7.4 was never made to handle the HP the 7.4 can dish out. A 5.7 is as big as you want to go.

 

[Pessemist]

Re: Help with prop hub spun issues

I would say you have to much engine for the prop. If this was a Bravo drive the prop hubs are made to handle more HP and torque. The 7.4 was never made to handle the HP the 7.4 can dish out. A 5.7 is as big as you want to go.

This is the original engine for the boat. The only change is the gearing for the stern drive (1.47. Vs 1.32)


Obviously Searay sold a lot of these boats before the Bravo drive came out, What prop might give me the best chance of not spinning hubs? Keep in mind that i drive this boat like a newborn baby and seldom beat it hard. Any suggestions?


Obviously swapping out engines is not cost effective.]

 

[alldodge]

Re: Help with prop hub spun issues

I would reduce diameter and increase pitch. You will get more slip but reduce the load. I would recommend reposting this in the prop section and let the prop dues have a wack at it. If you fix the hub so it won't slip then the drive will break. Google prop calculators and enter data about your boat, I tried but didn't have all the info needed (weight, length, fuel, etc)

 

[NHGuy]

Re: Help with prop hub spun issues

If you NEVER EVER hit anything you could put in a solid hub. The speed boat guys use them. Your big motor has so much torque that it's overcoming the hub's release value by the sound of it. I'll search the prop places to see if there are high torque hubs. I think Bravos and Alpha's use the same spline. That's what's puzzling about this.
If you generally plow around, running at 1300 to 2000 RPM for long periods that puts max load on the hub. The 1.47 gear takes a teeny bit of load off the drive, so little it really should not matter. But it does NOT make things harder for the hub.
I'd suggest removing the whale tail, running on plane or off, and avoid plowing. And if you just have to go 12 MPH get some trim tabs to keep the boat's nose down, not a whale tail. I'd also move any available weight forward in the boat.
You are smart not to hammer it, driving it easy will definitely preserve things. But do move smartly past the point of plowing when you can. When the boat's nose is pointed skyward is when the force is great on the entire drive line.
Keep the drive trim tucked all the way down unless you are flying her along. You want it all the way down until on a full plane and raising it will improve speed by lifting the bow.

 

[Pessemist]

Re: Help with prop hub spun issues

If you NEVER EVER hit anything you could put in a solid hub. The speed boat guys use them. Your big motor has so much torque that it's overcoming the hub's release value by the sound of it. I'll search the prop places to see if there are high torque hubs. I think Bravos and Alpha's use the same spline. That's what's puzzling about this.
If you generally plow around, running at 1300 to 2000 RPM for long periods that puts max load on the hub. The 1.47 gear takes a teeny bit of load off the drive, so little it really should not matter. But it does NOT make things harder for the hub.
I'd suggest removing the whale tail, running on plane or off, and avoid plowing. And if you just have to go 12 MPH get some trim tabs to keep the boat's nose down, not a whale tail. I'd also move any available weight forward in the boat.
You are smart not to hammer it, driving it easy will definitely preserve things. But do move smartly past the point of plowing when you can. When the boat's nose is pointed skyward is when the force is great on the entire drive line.
Keep the drive trim tucked all the way down unless you are flying her along. You want it all the way down until on a full plane and raising it will improve speed by lifting the bow.

I think you guys are on to something. It does usually 'let-go' when I am plowing..never when on plane. Am I correct in assuming that a Bravo I sterndrive unit uses the same diameter 15 spline drive shaft as the Alpha I?

I am having a hard time finding a prop rated for Bravo I stern drives. Searay originally called for a 15.25x15" prop for this boat with the 1.32 gear set. But I used a calculator and found that with my 1.47 gear set a 15.25x16" prop should give almost exactly the same performance. This is a 7.4 liter Mercruiser engine. The boat is a Searay 260 1988' Sundancer. Alpha I drive (My luck, the Bravo drive came out in 1989!)

To summarize, I have two questions: Do you guys think the 15.25x16" prop is the way to go? And will one sold for the Bravo I sterndrive also fit the Alpha I? (both 15 spline)

And who sells a good Mercruiser 15.25x16" Prop?! (I guess that's 3 questions...) I see several 15x16" but 15.25 diameter seems hard to get in 16" picth

 

[alldodge]

Re: Help with prop hub spun issues

I found this info on another forum I'm on which I hope will help.

From post of A.O. Razer
The Alpha and B1 has the same size hub/barrel and run the same props. The big difference is, that a boat with an Alpha will usually require one type of prop, where a B1 boat another. It boils down to the fact that the Alpha boats are normally smaller with less power and slower. If you run a Maximus or B1 prop on your Alpha there is a good chance you'll tear it apart. It is build for smaller diameter props that put less load on the drive compared to the Bravo 1. Regarding the rubber hub and the solid hub is a question about power and strength. Merc reccomends the impact absorbant rubber hub up to 380 hp and the solid hub for 400+ hp. There is also the XR 1.1/4" hub, and that will only fit XR size driveshafts.

Here is a list of the most commom uses of the different merc props. The order is random.

The props normally used on Alpha's are:
LaserII
Mirage+
Vensura
Revolution4
High Five
You can run the Maximus (15.25 or less dia.) and Bravo1 prop, but it is rare that an Alpha boat calls for this, and it can hurt the drive.

The props normally used on the Bravo 1, Bravo 1X, Bravo 1XR:
Mirage+
Revolution4
Bravo1
Maximus
Hydromotives, Herings ect.
You will of course see Bravo boats run some of the others as well, but these are the most common in high performance boating.
End A.O. Razer post

From my gathering it's best to keep the diameter under 15 inch. While plowing water this creates the greatest load on the hub. Could always go to your prop shop and ask to have a solid one put in like NUGuy mentioned

 

[Fun Times]

Re: Help with prop hub spun issues

I would reduce diameter and increase pitch. You will get more slip but reduce the load.

While it seems that you really shouldn't have to go down in propeller diameter I would agree that going down would be the next logical choice to a certain degree for testing purposes.

Am I correct in assuming that a Bravo I sterndrive unit uses the same diameter 15 spline drive shaft as the Alpha I?

Yes a standard bravo drive prop hub will fit your Alpha drive.

I am having a hard time finding a prop rated for Bravo I stern drives.

Do you plan on using aluminum or stainless steel propeller? Here are some lists of Mercruiser propellers,

Propellers | Mercury Marine
Online ordering of genuine Mercury Marine Propellers

Here is a list to consider
Compare | Mercury Marine

If you're going stainless steel then the vengeance has the smallest diameter that fits and works well with the Alpha style drives.

Also be sure to get Mercruiser Flo Torq Solid Hub Kit 835258K 2 that handles the 400HP+, 1" prop shaft because FLO-TORQ Hub Kit 835257K 1 is rated for under 400 HP which should still be good enough for your boat but it appears you have some type of unexplained phenomenon going on so bigger should be better.

Sea ray originally called for a 15.25x15" prop for this boat with the 1.32 gear set. But I used a calculator and found that with my 1.47 gear set a 15.25x16" prop

Although a bigger diameter propeller would work better on your boat model the diameter that is up for suggestion would come down to the 13 - 14.5 range vs the bigger 15.25 diameter.

Here's a fun Boat Propeller Calculator,
Propeller Calculator / Prop Calculator

And who sells a good Mercruiser 15.25x16" Prop?!
I see several 15x16" but 15.25 diameter seems hard to get in 16" picth

Mercruiser does not offer an 15.25x 16" propeller, so you would have to go with an aftermarket Propeller for that size option and google search engine is your friend. 15.25x16" proppler - Google Search

 

[Pessemist]

Re: Help with prop hub spun issues

OK guys, one final question:

I pretty much think I had prop hubs in the past that could not handle the 7.4 liter 310hp of the mercruiser mated to the Alpha 1.

The last prop was 16x16 aluminum and I really liked the performance. Searay originally called for a 15.25x15 prop but the gearing was changed (by me) from 1.32 to 1.47 in the Alpha 1.

To take some of the strain off the hub I wanted to go to a 15.25x16 prop but I can't find any in that exact size.

Right now I am looking at a 4-blade 15x16. I mostly cruise around just on plane and so I want to get on plane asap and top speed is not a concern.

This prop & hub is rated for the Alpha 1 up through 350hp (the 7.4l is 310).

I am thinking OK with this? Boat is a 1988 Searay Sundancer 260

Michigan Wheel Vortex XHS Aluminum Boat Propeller #992202 for Mercruiser Sterndrive Bravo One 7.4L 300 - 330 HP - iboats

 

[Fun Times]

Re: Help with prop hub spun issues

This prop & hub is rated for the Alpha 1 up through 350hp (the 7.4l is 310).

I am thinking OK with this? Boat is a 1988 Searay Sundancer 260

Michigan Wheel Vortex XHS Aluminum Boat Propeller #992202 for Mercruiser Sterndrive Bravo One 7.4L 300 - 330 HP - iboats

While the Michigan wheel vortex propeller is a nice popular aftermarket propeller at a good price, In my opinion I personally feel that after everything you've been through so far you would most likely have slightly better overall results going with the Alpha 4 propeller especially since you plan to stay with an aluminum propeller vs stainless steel.

Boat Propellers, Mercury Propellers, Mercury Outboard Props, Mercruiser propelle - Mercury Performance - Mercury Alpha 4 Propeller 16 P