Advice needed *UPDATED*

[blackhawkdc]

Ok folks, I realize that I really don't have any information to give you other than what I have for a boat and motor. My guess is that the prop that I have is too big for my setup. Here's my setup: I have 14' 1971 Crestliner Sea Scout (Standard aluminum hulled runabout). It is powered by a 1971 Johnson 50 horse twin. Someone out there has to have something similar. I plan on using the boat for recreational boating, along with tubing/ kneeboarding, and possibly skiing. I don't have a working tach, and my speedometer reads one of the following 5, 15, or 20mph. I hope to get out this weekend on the lake with my timing light with a built in tach and see what WOT RPMS are with the current prop.

Here are my questions: What can I expect, approximately, for a top speed? What would be a good guess for the proper sized prop? I'm currently running a 13 3/4" x 15 aluminum prop, slightly beat up. I'm not looking for specifics of course, just rough estimates. Also, would a Hydrofoil or something similar be beneficial?

Thanks in advance!

Seth Petro

 

[blackhawkdc]

Re: Advice needed

Re: Advice needed

Ok, I was able to get the boat out on the water this evening and get a WOT tach reading. She ran at 5200
RPM's. Still unsure as to speed though, speedo still not accurate. Awaiting the arrival of a new set of gauges. 5200 RPM's was with only myself in the boat and a full (6 gallons) tank of gas. Boat planes out well and has a decent hole shot. Rides pretty level on plane. Also, the AV plate is level with the bottom of the hull.

Is this a good reading for this motor? Or should I be investing in a less aggresive prop, say a 13.75x13? I plan on using this boat for kneeboarding and for tubing. I have had three guys in it with a 4th guy on a kneeboard and it did alright. But if the kneeboarder is on the heavy side and not adept at kneeboarding yet, the boat has a hard time getting on plane.

Any suggestions? Maybe a prop that'll help get a little better holeshot, or get the boat up on plane under load better? Thanks!!

Seth Petro

 

[Dhadley]

Re: Advice needed

Re: Advice needed

Those motors are one of the ones that don't really like to be set up in the low 5000 range. They live much longer set up at 5800-6000 with an average load.

Now, a 15 would probably be a good starting point given you do a lot of water sports. But, if it's beat up / worn we aren't going to have a lot of success with changing the set up before it starts venting.

Obviously testing will tell us what we need to know. Do you have access to a 15" ss prop that you could try?

 

[blackhawkdc]

Re: Advice needed

Re: Advice needed

DHadley,
Thanks for the reply. So you are recommending that I run the engine in the 5800-6000 RPM range? My manual states 5500 RPM recommended WOT. Unfortunately, I don't really have access to a 15" SS prop that I can try. I currently have the OEM original 13.75x15" prop on it. Not in bad shape, but knicks here and there. Probably old technology too. Isn't a general rule of thumb that when switching from an aluminum prop to a stainless steel, you usually step down a pitch size? Just curious, this is all new to me. First boat that I've owned and just happy to finally have it running good.

So, to condense everything. I'm currently running a 13.75 x 15" OEM Aluminum prop on my Johnson 50 horse. The motor runs at 5200 RPMs WOT with just me(165lbs) in the boat. I'm going to take the boat out this weekend with my and a buddy fishing, I'm going to bring a long a handheld GPS to varify speed. But I believe the boat to be doing about 30-33MPH. I don't experience any ventilation around curves. the motor is set up with the cavitation (?) plate level both in height and plane with the bottom of the boat. The boat seems to plane out easily and level.

Now I'm happy with the performance when its just hauling passengers, but would like some more pulling power for pulling a skiier/kneeboarder/tuber.

What are your recommendations? Prop size and pitch, certain models, SS or aluminum. Money is an issue, as I onlt have so much allotted to the boat and it needs all new seats and carpeting.

Thanks again Dhadley! Its nice to have such expertise at my fingertips. Thanks!

Seth Petro

 

[walleyehed]

Re: Advice needed

Re: Advice needed

I don't want to hi-jack Dhadley's Response, but I agree totally with the 5800-6000. Yes, the manual says other-wise, but the fuel was much better in the era the engine was built than what we have today.
Follow his advice...his experience is priceless.

 

[Dhadley]

Re: Advice needed

Re: Advice needed

When folks say to drop a size in pitch when going from aluminum to stainless, that's only part of the story. If you go from an old technology aluminum (beat up) prop to a new technology ss prop without changing the set up, yes you probably will have to drop a size. They probably forgot to tell you the part about the set up, huh?

In this case the set up isn't the greates to start with. With a top rpm of only 5200 the holeshot isn't going to be the best anyway. And adding a water toy only compounds the strain on the motor.

So, to get the rpm's up we have 2 choices.

1- drop pitch. That's fine for watersports. Most ski-type boats have 2 props anyway. One low pitch for pulling power and one for cruising.

2- Max out th set up. You may still end up with two props but the motor will be much happier.

Another handicap we're working with is that, I assume, we have no power trim. That's OK but obviously it'd be better with trim. Especially for holeshot when pulling toys.

I would start with a decent ss 15 like a Stiletto. That will allow you to raise the motor some on the transom. We can raise it now but I would expect the current prop to lose bite. Raising the motor will reduce drag which improves performance across the entire rpm range. from holeshot to top end. It gets the efficiency numbers up basically.

 

[blackhawkdc]

Re: Advice needed

Re: Advice needed

Thanks to both of you for your advice. I'm taking the boat out again this weekend, so I will look into playing with trim and see if I can't raise the motor up a hole, if I have adjustability on this one. You are correct that there is no power trim on it. I kind of figured that I'd end up with two props. One for just cruising and one for heavy loads. I'll start keeping my eyes open for a SS prop in the 15" pitch range. In the least, I need to at least replace the OEM prop that's on it.

Thanks again for the advice and I'll get back to you both with what I can figure out this weekend.

Seth

 

[blackhawkdc]

Re: Advice needed

Re: Advice needed

Ok, well, I'm back from the lake with more figures. As far as I can tell, my motor has to provisions for adjusting height, but it does have 4 holes for adjusting trim. I tried different holes and ended up coming back to the hole that it was in before. I was able to get slightly more RPMS (approx 50) by having the motor trimed all the way back and up. But then the handling started to get a little iffy. It also seemed to launch the bow of the boat up and out of water more, but still seemed to plane alright. I trimmed the motor down and it had a harder time planing out and didn't do much for RPM's either. I'm still running 5200 RPM's WOT and now have a speed reading too from a handheld GPS. Max I could get for speed on a smooth lake with just myself in the boat was 29.8MPH.

Now I just ordered a TP Hustler alu prop in 13.75x15 size. I'm hoping that this new prop will help things out. I thought about SS, but I just can't afford that kind of purchase. I'm half expecting to still need to purchase a second 13" pitch prop for loads, but am hoping the new Hustler 15 will help out.

Any other thoughts and advice for me at this point? I have a new set of Teleflex gauges coming in the mail. First set of gauges I've been able to find with the look that I want.

Thank you all,

Seth

 

[Bry21317]

Re: Advice needed

Re: Advice needed

Seth,
I have a 17 pitch Hustler on my 19 foot Bayliner with a Force 125hp engine. This is a great prop. I just purchased the Turning Point Express SS and It was sent back today. The SS prop on my engine and my setup made me lose all of my Hole shot and also lose about 10mph off the top end. With that new SS prop, my boat was slow as dirt. I couldn't get over 33mph on GPS, where as with the Hustler 17 pitch I am running about 42-43 mph on the top. The boat jumps right out of the water with the Hustler.

So I think you will be very happy with the Hustler prop. I have ordered a 15 pitch to try, as I can't get my RPMS up in the top of the range.

Hope you like it.

Bryan

 

[jack7771]

Re: Advice needed

Re: Advice needed

I have a 110 hp Evinrude on a 16' Starcraft, and use 2 props, a 15" & 17", both aluminum TP Hustler props. We do a lot of water skiing, and the lower pitch 15" prop is best for that, especially slalom skiiers. With the motor tilt all the way in, that prop at WOT is 5400 rpm and 35 mph with 4 people in the boat. With it tilted out to the 3rd setting and using the 17" prop, the boat will do 42 mph.

Jack

 

[blackhawkdc]

Re: Advice needed *UPDATED*

Well, here's the latest on the boat/prop situation. Purchased a new Hustler Turning Point prop. 13.75"x15". No change in engine RPM's, slight increase in speed. 29mph now versus 28 before. Figured about 20% slip. Played with trim on the boat. Trimmed all the way up, hit 5400 RPM's and 31mph, but ventilated on the holeshot, too much bow lift also. So, as it sits right now, 29MPH is the top speed at 5200 RPM's. Tach reading is with a Mac Tools digital automotive timing light/tach set to 2-cycle. No ablity to raise motor without unmounting brackets and raising up on transom of boat with shims.

Any advice for me to get more out of this setup? I don't think I'd really be able to raise the motor on the transom as the forward mounted clamp plate is resting against the aluminum top plate on the transom. I'm assuming that I'm really going to need to purchase another prop, a 13" pitch prop to gain more R's.

Any thing else that I can try? Thanks in advance! And thanks also to those of you who have helped me so far.

Seth

 

[walleyehed]

Re: Advice needed *UPDATED*

One item of interest here that I'm begining to see a pattern of is the Hustler prop pulling harder than an SS counter-part, or even an alum of the same pitch.
The hustlers I have DO have very aggresive cuping, and I am starting to think they are trying to get the efficiency up against all other aluminum props....no problem, but the Hustler is running the same RPM in several cases I see, as a prop stamped 2" higher in pitch.