Can't find a prop anywhere

[inthedirtagain]

I have a 1966 Starcraft Holiday 18ft, with the original Evinrude Starflite 100-s o/b. I'm trying to re-prop this combination because I seem to be over-propped. I've run a best of 29.7mph verified by GPS, but WOT is at 4700rpm. This is with 2 adults, 2 kids, roughly 10gal of fuel, and 2200-ish ft elevation (Boise area). I'm estimating the hull/engine weight to be about 1200lbs, with a "dead" weight of 550lbs. The current prop is a 3-blade, 12x14 alum in decent condition (no major chunks or bends). iBoats shows I should have 14x11, as do other sites, but I can't find one. This is the pin-drive, non-thru hub exhaust model. I'd like to get my rpms up around 52-5400 range, if possible. Can anyone help locate a source for me?

I've got the cav plate about even with the bottom of the boat, and have also messed with trim settings. I've got a solid transom confirmed by core samples, but have yet to check the condition of the foam for saturation. That's next if I can't locate a good prop. The boat will be used for both tubing and fishing. So far, it planes quickly. I'll also do a compression test this week. Others have reported 33-38mph, so this is what I'm shooting for. Thanks

Bif

 

[inthedirtagain]

Re: Can't find a prop anywhere

I performed a compression test this morning and all 4 cylinders are reading ~100psi both cold and warmed-up. Until my manual arrives in the mail, I'm not even going to attempt to look at the timing advancements under varying throttles. To the best of my limited marine 2-stroke knowledge (I am a certified diesel mechanic, though), this engine is performing as it should. The problem lies in the prop size/pitch, in a possible water-logged floor, or both. Still can't find a prop. Thoughts?

 

[inthedirtagain]

Re: Can't find a prop anywhere

Ok, so in an effort to get people to actually respond, I'm going to throw this question out there:

Suppose that I could actually find any size prop imaginable for this boat and O/B combination, what would you recommend?

 

[steelespike]

Re: Can't find a prop anywhere

If my math is right and I have your gear ratio right at 2:00. I have a feeling you may be at or over 5000. You may want to verify your tach.I have you at over 30 mph @ 4700. After deducting 10% slip puts you at about 27mph.I feel for you to have almost 30 mph your motor needs to be turning more rpm.
You could also verify your ratio by removing the plugs and count flywhell turns for one revolution of the prop. At that age I think its obvious prop selection will be limited. You should watch Craigs list and post a wanted on craigs list also your local swap sheet.
Ask in the free webvertize at www.aomci.org Also watch on ebay
I've bought outboards, and bought and sold outboard and marine parts there with good results.Just check the feedbacks and return policy if any.
In desperation you could have the prop repitched a little.
but verify the tach before anything else.

 

[inthedirtagain]

Re: Can't find a prop anywhere

Thanks for the heads-up on that website. I'll give it a look over later tonight. The original tach on the boat is not functional, so I ran the motor through my engine analyzer from my shop. It doesn't have a provision for 2-stroke, so I left it on the 8cyl setting (O/B is a V4). Its an older analog model that works well for reading the point gap/dwell, and the general condition of ignition systems. I use it to tune my 66 Mustang convertible, since I still use the original distributor w/points-style ignition. I'll be purchasing another tach to install into the dash later this week, so the rpm will be confirmed by a second (and much newer) tachometer. Still, I prefer the classics! Thanks again.

 

[inthedirtagain]

Re: Can't find a prop anywhere

I bought a new tach to test against my analyzer. I'll have it mounted with a test run completed in the next few days. If the analyzer is innaccurate, that will be a sigh of relief because I can find props with a higher pitch fairly easily, but not one with less pitch than 14. If this motor wasn't in as good condition as it is, I'd look to swap it out with something newer.

 

[hwsiii]

Re: Can't find a prop anywhere

inthedirtagain

We need some good RPM and GPS numbers at wide open throttle to see how close the prop you have now is to what your boat requires. Get us some good wide open throttle GPS numbers in opposite directions with the RPM, and lets see how dose you are now to where you need lo be,


H

 

[inthedirtagain]

Re: Can't find a prop anywhere

Once I get the new tach installed, I'll go out and get some more info. To the best of my knowledge, my analyzer should be accurate.

 

[inthedirtagain]

Re: Can't find a prop anywhere

So now I've got the new tach installed and have had a chance to get out on the lake. There was a little more wind and chop than I would have liked because we were unable to to break planing speeds for most of the trip. On a few occasions, I was able to open it up and get some numbers. With 4 adults, 12gal of fuel, and a cooler full of food, I was able to reach a maximum of 31mph (GPS) @ 5700rpm. Also had to trim the motor all the out.

Knowing this, I think I'm under-prop'd. I've got a local shop nearby with a 13x15 SS in nice shape, and he wants $150 for it. I have struck out on Craigslist, and will now check out Ebay. If I were to pick up the SS prop, what difference will I see compared to the 12x14 alum? I know that I'll pick up a little more speed, lower the rpms a few notches, and sacrifice some holeshot, but more specifically, I'd like to know what going to SS would do. Thanks for all the help, it is really appreciated!

 

[steelespike]

Re: Can't find a prop anywhere

Its hard to give an accurate estimate of an improvement going from al to ss.
No doubt the ss "should" help overall performance but how much is difficult to estimate.
Hopefully H will be along, he is sharp and may be able to help tell if the ss is a good choice
or offer another selection.

 

[inthedirtagain]

Re: Can't find a prop anywhere

I found a 12.5x16 alum on ebay (NOS) for $60, so I went for it. Hard to find this kinda stuff, so I'm not going to delay.

 

[steelespike]

Re: Can't find a prop anywhere

That could be a nice find.We'll be looking forward to your results.

 

[inthedirtagain]

Re: Can't find a prop anywhere

Well, my 10yr old GPS finally took a header today, just when I was about to try out the new prop (fast shipping!). I lost my holeshot, but I expected that. What I wasn't expecting was how much top-end I picked up. Couldnt tell you exactly how much without the GPS, but it was substantial. What is interesting is that the boat still wanted to hit 54-5500 rpm most of the time. Makes me curious if I could also pull a 17p for even more speed. Don't think I need to though. I'm happy with what I've got now. Thanks for the help everyone.

 

[steelespike]

Re: Can't find a prop anywhere

The ss prop is cleaner through the water and usually provides more lift getting more boat out of the water. This can allow more rpm and speed.
There are ss props that load a motor more than al props I'm not the guy that can explain why.Perhaps too much of a good thing like cup or rake.

 

[inthedirtagain]

Re: Can't find a prop anywhere

So my GPS magically started working again. I took the boat out fishing this morning with just me and the dog. I got a best of 31.5mph @ 5600rpm. Still expected more, but I can live with it.

 

[jimmbo]

Re: Can't find a prop anywhere

Your engines gear ratio is 16:28, WOT range 4500 - 5500. Since your outboard shares its gearcase with the older electric shift omc stringer stern drives you might consider looking at those props. On the sterndrive props the diameter does not shrink as the pitch goes up. It will load the engine up more. Just check to make sure the blades do not hit the water pickup.
As for stainless... sometimes they are faster; thinner blades - more efficient, more rake - help hold the boat higher out of the water, more cup - better grip on the water allowing higher mounting on transom and higher trim angles. A couple of negatives about Stainless.. Heavier - more stress on shift mechanism, and unlike Aluminium where the blades often snap of on impacts, stainless blades will bend eventually into the shape of a steel ball

 

[inthedirtagain]

Re: Can't find a prop anywhere

I'm going to fix the boat up just enough to sell it next season. My wife wants a bowrider and something a bit newer. I can't say as I blame her, so I'm done searching for more speed. Anything I spend on it now is only going to be for beautification purposes. Its fast enough for fishing and pulling kids on tubes. Thanks for all the help on this one.