Prop help for 26' Stamas

[CITM]

I have an issue that I?ve been struggling with for some time and hope you guys can help. I trashed a prop that worked pretty well and have struggled to find the right one since. The one that worked was a 15 1/4x15 Black Max. I tried a Quicksilver of the same dia and pitch and it didn?t work, RPMs were way too low. Another I tried was a 16x14 aluminum (don?t recall manufacturer but RMPs were too high and speed too low).

My goal is to increase RMPs without losing (or possibly gaining) speed. My current setup is OK with a light load but with a heavy load it struggles to get on plane (any conditions), and stay on plane when it?s rough. Heavy load for me is 5-6 people plus coolers, etc = 1,000-1,200# +/-. I installed trim tabs and they help a little but not enough. It seems to ride high in the bow with the current setup.

My current prop is a stainless 14?x15 Turbo, I?m not sure of the model.

WOT with an average load is 4200 RPM @ 27 MPH. Heavy load is 3800 RPM @ 24 MPH. I belive my max RPM is 4600-4800 RPM.

Engine is a 260 HP Merc I/O with an Alpha drive.

Boat is a 1984, 26? Stamas Sport Cruiser. Dry weight is 7000# according to Stamas. Loaded and full of gas I assume it?s a little over 8000#.

Like I said, I?ve tried several props so I know it?s not all about diameter and pitch but I?m not sure where to go from here. I?m considering trying another Black Max but they don?t make the exact model any more so who knows how it would work. I also see Solas makes a 14 3/4x15 four blade. And I read on another thread that a Mirage might be a good choice for heavy boats to help with stern lift.

 

[steelespike]

Re: Prop help for 26' Stamas

Heavy boats can produce a lot of slip a 4 blade can help resist slip.
I have seen very good results with the Solas amita 4 blade.Resists slip,better hole shot,stays on plane with less power.Better control at dock side.

 

[CITM]

Re: Prop help for 26' Stamas

Thank you. It looks like the smallest and shortest pitch Solas Amita is 14 3/4"x15". Do you think I'll achieve increased RPM's with this over the 14 1/4x15 stainless Turbo I'm running now?

 

[steelespike]

Re: Prop help for 26' Stamas

In rereading your post I have to wonder why we need to struggle to make rpm.
with what appears to me to be a normal size pitch.It doesn't seem to me they would set a boat up that needs a prop from almost the bottom of the list.
To make 4600 you would have to go to a 13 and there is only a 12 after that
That wouldn't leave any flexibility for special requirements as you have discovered.
I think you have other problems.Motor may have problems or perhaps the bottom is dirty or rough.I think you should be able to make rpm with a 15.
Depending on your gear ratio it might even make it with a 17 if not loaded too heavily.If you think I'm nuts then imo the alternative is a 15 stainless 4 blade and have it reworked to a 14 or 13 or have some cup removed.I say stainless because
changing materials creates more variables.You could have the Solas reworked as well
but the material change might leave you with additional problems.
Changing design,materials and brand makes things more unpredictable.

 

[CITM]

Re: Prop help for 26' Stamas

The thought that something else is going on has certainly crossed my mind but I don't know where to start. I've had about everything rebuilt - engine, drive, carb (reman). Bottom is painted w/ 2000e & vc17 and its a trailer boat. I just checked the plugs and they look good. Just replaced the fuel filters and distributor cap. Plug wires are pretty new. I will say that I didn't see any improvement after the engine rebuild and it had very low compression in one cylinder prior to the rebuild. Maybe they messed something up but I trust the shop that did it. Maybe a compression check is in order.

I called Stamas but they didn't know what prop was on it originally.

Thank you again for your help.

 

[Tail_Gunner]

Re: Prop help for 26' Stamas

WOT with an average load is 4200 RPM @ 27 MPH. Heavy load is 3800 RPM @ 24 MPH. I belive my max RPM is 4600-4800 RPM.

Your a bit all over the place....That turbo has a lot of bite........i wonder if your going to lose hole shot and top end.....with a 15..doesnt sound like a plan

Umm that it....

 

[CITM]

Re: Prop help for 26' Stamas

Sorry I meant my max RPM is supposed to be 4600-4800.

 

[Tail_Gunner]

Re: Prop help for 26' Stamas

yes i know...but you have to understand that your going to prop for max load or average load.....Is that your boat

 

[steelespike]

Re: Prop help for 26' Stamas

Agressive use of the trim tabs could slow things down.Once on plane have you tried for max speed with the tabs out of the water and then carefully added?
I think a couple of test runs with one or 2 aboard,tabs up, tabs in play. with max rpm and speed,hole shot description,lowest planing speed.Check that it is timed correctly and that it advances as it should.Compressin check wouldn't hurt. Is carb opening all the way.Try weighing it hopefully with any weighty extras removed Weigh trailer then boat and trailer or vice versa.
We're looking for absorbed water.Have you added a flow meter or fuel management system?

 

[CITM]

Re: Prop help for 26' Stamas

yes i know...but you have to understand that your going to prop for max load or average load.....

I think that's what I am trying to do. Here's my boat.

 

[CITM]

Re: Prop help for 26' Stamas

Agressive use of the trim tabs could slow things down.Once on plane have you tried for max speed with the tabs out of the water and then carefully added?
I think a couple of test runs with one or 2 aboard,tabs up, tabs in play. with max rpm and speed,hole shot description,lowest planing speed.Check that it is timed correctly and that it advances as it should.Compressin check wouldn't hurt. Is carb opening all the way.Try weighing it hopefully with any weighty extras removed Weigh trailer then boat and trailer or vice versa.
We're looking for absorbed water.Have you added a flow meter or fuel management system?

I just added the trim tabs with the hope that it would help with this issue. They do help a little but not much. I did exactly what you described above. Agressive use did slow it down.

I'll check timing, advance and compression. Carb opening all the way is a good question.

I bought a fuel flow meter but don't have it installed yet, I'll get that done.

Weight is a little tougher but I'll work on that too.

I'll check back with info as I gather it. Thank you again.

 

[steelespike]

Re: Prop help for 26' Stamas

As far as the fuel flow meter there was a post here somewhere where they unknowningly lost a couple of mph after installing a fuel maagement system.
Probably messed up the install some how; but removed it a gained back his lost speed.No bearing on your issues at this point.

 

[CITM]

Re: Prop help for 26' Stamas

Update:

I posted a new question in the Merc engine section with updates on this issue. http://forums.iboats.com/showthread.php?p=2822292#post2822292