Yamaha 115 2 stroke SV1900CC prop starting point

[sledge437]

I did search the forum for this topic but all other posts differed slightly with most having 4 strokes or different hull. I recently purchase a 2001 Sv1900 with a 2002 Yamaha 115 2 stroke. I went through the motor with carb rebuild, fuel lines and filters, ect and the motor runs great. The prop on it is a four blade stainless with NO markings...I mean none!  I checked inside the hub, the outside, the entire prop......not stamped, not labeled, 0, nunca, nada, zilch and former owner is of no help. With it at WOT of 5000rpm, I'm getting a decent hole shot but only 35mph wot. It grips well in turns and handles chop ok... fuel economy, even for a carb'ed motor is terrible. Ive experimented with different trim and jack plate settings as well. 

Should I expect more speed? I know its not a speed rig and I don't need one but I would think IMO overall performance could be increased with a different prop. Most use of the boat will be freshwater lake cruising with 2 people maybe towing an occasional tuber. 

Can anyone, with a like rig, give many any ideas on a good starting place on prop(s) to start experimenting with? 
Thanks in advance. 

[Juan]

That's weird. I've never heard of a prop that didn't have the size and pitch stamped somewhere on it. It sounds like your 4 blade is doing what it is designed to do and I'd probably keep it if I were pulling tubes or skiers but you're right...performance could be better. A 3 blade prop is normally the best prop for all round performance. Can't help ya with the size you need because it depends on several factors, boat design, weight, rpms, and engine gear ration to name the most important..
You can determine the diameter of your current prop by measuring the radius of the prop from the prop shaft center line to the tip of one blade then multiplying that measurement by two.
A propeller shop can tell you the prop's pitch by measuring the propeller or by using a pitch block and they can recommend the best prop or you can use one of many prop calculators on the internet based on the factors above.

[sledge437]

10-4 Juan. Good points.  Thanks for the reply. Ill measure it tomorrow. I was hoping someone had the same hull and motor to give me starting point as well. 

[Juan]

I think there are some forum members with the same set up, so maybe they will chime in, but even with the same set up, the prop they run might not be the prop you need to get the best performance.
4 blade props are usually more expensive than 3 blade props and since you don't know the size and pitch of yours, why not take it to a prop shop where they can tell you what size it is and make a suggestion on which prop you need for best performance? Prop shops normally have a variety of props that they will let you try out until you find the one that works best for your set up and I'll bet they would be happy to swap the correct sized 3 blade for your 4 blade.

[gnrphil]

With what I've seen with similar but slightly heavier boats I'd expect to see about 45mph with a 13x19 ss prop.

[sledge437]

Thanks everyone. SC, your dead on. Suggested high rpm is 5500 on that motor. Great starting points guys and solid advice.......and I measured diameter today at 13.5". Still no pitch markings so I'll take it by and have the pitch checked. Thanks Juan on possible trade advice. I have access to a 13x19 stainless so I may slap it on and take it for a spin to check that one. I'd be happy with an "ok" hole shot and a WOT closer to 40. I think my fuel economy could improve as well. Gnrphil, I appreciate the optimism!

[gnrphil]

Looking forward to the results, check your motor height while your at it.
Oh and use an analog speedometer, they're always faster  emthup

[985crabs]

Just checked my setup. I've got a 14.25" X 19. My motor is a little larger at 150 hp, but it should work for comparison. WOT is 5,500, though I've never approached that. My boat will go 40 mph at under 4,500 RPMs. That's been fast enough for me. I put a hydrofoil on the cavitation plate and I am almost immediately on plane from hole shot. Very important for marsh fishing in 18" of water. Fuel economy? 3-3.5 mpg. Not such an issue now that non-ethanol fuel is below $2.50/gal.

Crabs

[sledge437]

Thanks crabs. I sometimes wish i had a 150 hanging on the back.....

[sledge437]

So had prop pitch checked this morning and its a 13.5x16p 4 blade. Prop guy thought the prop should be just right. He couldnt find a pitch or maker stamped or labeled either so I dont feel too badly. He suggested taking the hydrofoiil (shallowblaster) off and running it again. I dont see this having a huge effect on lack of rpm, speed and efficiency, but its easy enough to do. He says he has seen it where some setups dont need or like a hydrofoil. Its off now. Headed to the lake. Ill post up the findings.

[sledge437]

You're right SC.
So pulled hydrofoil off and :
holeshot slightly slower, little bow rise, but still decent....I should have timed it but forgot
WOT 5100 rpm 38mph by gps. I unfortunately didnt have time to observe fuel efficiency. The boat seemed to plane slightly later at about 16mph and could maintain 19mph or so on plane.
seemed to want to porpoise a little sooner while trimming up but still, Im pretty happy with the improvement.
Still good grip in turns.
Think I'll try that 13x19 this week just to see...

[gtightline]

I'm running a 13x19 aluminum on my Yamaha 115 on a 180CC. At WOT I turn around 5500-5600 rpm with a top speed of 47-48 mph...I very rarely run that motor wide open, it cruises real nice at about 35 mph and is really good on fuel...just saying.

[sledge437]

You've got that boat dialed in! Really nice numbers. Hoping mine will be close. It'd be nice to have that kind of performance for cruising and the 4 blade I have now for towing and bays. Thanks for the info! I know the SV may not be able to duplicate Bc of hull's difference but getting close would be nice. It's encouraging.

[gtightline]

I'm telling ya, that little 115 Yamaha has been a good motor....

[Juan]

I've got a 13.5 x 21 on a Mercury 115 mounted on an old bass boat I recently picked up.. according to the gps, it's running right at 50 at WOT (5300 rpms) but it will turn a lot more rpms than recommended so I need to drop the rpms down a bit.. Mercury and Yamaha props are interchangeable. The funny thing is, I found a 15 spline, 4 blade stainless steel prop at the local flea market today that I believe might increase the performance and drop the rpms...it looks to be in good shape and the guy only wants $60... but I couldn't find the size on that prop either... I'm going back tomorrow with a magnifying glass and looking again.

[gtightline]

Hey Juan, $60.00 sounds like one heck of a deal for that prop.There is a place in Ft.Lauderdale that I have purchased props from in the past. They have new and refurbished props and used in good condition...I'm sure you have heard of this outfit before, they have a good reputation, Frank and Jimmie's....

fjprop.com/page/Fort_Lauderdale/45/16/

[sledge437]

Thanks all for the replies and info. I do appreciate it. Unfortunately, I haven't made back out to try the other prop but it sounds like it might work well. 50 is scootin' with a 115, Juan!

[Juan]

Apr 5, 2015 10:35:02 GMT -6 sledge437 said:

50 is scootin' with a 115, Juan!

The boat only weighs 881 pounds... it should scoot better than it does with fewer rpms.
I went to the flea market to take another look at the 4 blade prop... CLOSED . I forgot it's EASTER Sunday!

[sledge437]

Apr 5, 2015 11:41:17 GMT -6 Juan said:

Apr 5, 2015 10:35:02 GMT -6 sledge437 said:

50 is scootin' with a 115, Juan!

The boat only weighs 881 pounds... it should scoot better than it does with fewer rpms.
I went to the flea market to take another look at the 4 blade prop... CLOSED . I forgot it's EASTER Sunday!

Ah, the ol' power to weight ratio principle.

[erniet17]

I also have the SV1900 but with a 2005 Merc 115 4 Stroke. With a 14.25 X 17 3 blade I'm at 39MPH. With the Prop that was on the boat from the factory I was only hitting about 28MPH.