Prop Selection- Now with Tach!

[java230]

Re: Prop Selection- Now with Tach!

Those calculators unfortunately don't take into account the effect of a 1.75 inch increase in diameter with the 9 pitch. Try punching in 11 instead of 9 in the pitch number and see what you get. Also, the slip will be reduced; by how much is the question. Only testing will answer that question.

With the 14, you're showing like 23% slip, which is pretty bad(pontoon territory). The reason is because the prop has too much pitch(angle of attack) and too little shaft speed; so it's stalling and losing thrust. I wouldn't be surprised to eventually see cavitation burn marks on that prop.

Now that you say that I do see almost flakes or bubbles where the paint is missing all over the prop. I thought it was from salt exposure.

It's late, so I'll need to be brief.

1st- you're so far away from the peak HP at 3800, the 200 rpm/inch rule of thumb isn't applicable. You will see much higher RPM's per inch of pitch. You may be making 28HP at 3800 or 33HP at 3800, but certainly not 40HP.

That said, I don't think a prop is your problem at the moment. A 14" prop is very reasonable for that setup and it should easily run 30mph.

I'd start with motor and check compression. If you don't have a tester, you can do a cylinder drop test by checking rpm loss when a plug wire is removed from a cylinder. If needed, just by ear is fine.
Your carbs may need cleaning.
What is the history of the boat?
Since you indicated you can easily lift a side, it doesn't sound water logged.
Just an fyi, a 20hp on an 80's 13' whaler would run 28 and a 40 would run 35+.

I'll try to check compression next week. But it runs great. I'm afraid it might have some water..... I weighed it on the trailer, with a tank of gas, battery and anchor etc, and it was about 700lbs....

Thanks for the help!

 

[dazk14]

Re: Prop Selection- Now with Tach!

Now that you say that I do see almost flakes or bubbles where the paint is missing all over the prop. I thought it was from salt exposure.

I'll try to check compression next week. But it runs great. I'm afraid it might have some water..... I weighed it on the trailer, with a tank of gas, battery and anchor etc, and it was about 700lbs....

The bubbling is from salt exposure.

If you want good help, you'll need to answer my history question...Lousy help is always available.

 

[java230]

Re: Prop Selection- Now with Tach!

I have recently purchased the boat. I don't have any history other than it was owned by the sailing club at a local lake, before the guy I bought it from.

It's in decent shape no big holes etc, a couple of dings but they have been repaired. It appears to have been done when they happened. The gel coat is quite weathered. The only bad spot was the fiberglass under where the gad tank sits. It was cracked badly, but the foam was mostly dry in that area. It was probably repowered at some point as the controls are mounted on the left side of the console, and the cabling was run a look he floor and thru a hole that I don'trthink was factory to the back.

Is there anything specific that I can try to answer?

 

[dazk14]

Re: Prop Selection- Now with Tach!

Now that you say that I do see almost flakes or bubbles where the paint is missing all over the prop. I thought it was from salt exposure.




I'll try to check compression next week. But it runs great. I'm afraid it might have some water..... I weighed it on the trailer, with a tank of gas, battery and anchor etc, and it was about 700lbs....

Thanks for the help!

Are you saying the 700lbs. includes the trailer? If not, what system did you use to arrive at the weight.

Did the seller indicate to you that the boat ran faster than 20?

I ask because few owners would leave a poorly performing prop on it long enough for the paint to start blistering - although a Sailing club would be one of them. They hate "Stinkers" as a whole.

Have you pulled the plugs?

 

[jestor68]

Re: Prop Selection- Now with Tach!

When you're dealing with a 31 year old motor, you can't realistically compare it's performance with some performance review that deals with a brand new motor.

While that might be "lousy" advice(according to you know who), I believe it to realistic advice.

 

[java230]

Re: Prop Selection- Now with Tach!

Are you saying the 700lbs. includes the trailer? If not, what system did you use to arrive at the weight.

Did the seller indicate to you that the boat ran faster than 20?

I ask because few owners would leave a poorly performing prop on it long enough for the paint to start blistering - although a Sailing club would be one of them. They hate "Stinkers" as a whole.

Have you pulled the plugs?

Yes includes the trailer. Weighed each wheel and tongue with bathroom scale.

Pulled the plugs, they looks fine, but not recently replaced.

When you're dealing with a 31 year old motor, you can't realistically compare it's performance with some performance review that deals with a brand new motor.

While that might be "lousy" advice(according to you know who), I believe it to realistic advice.

Agree it's not a new motor. I just want it to last a few years, I'm really Ok with 20 mph. It's not bad. I don't think he owned it long, was recently paralyzed and bought a toon.

 

[dazk14]

Re: Prop Selection- Now with Tach!

When you're dealing with a 31 year old motor, you can't realistically compare it's performance with some performance review that deals with a brand new motor.

While that might be "lousy" advice(according to you know who), I believe it to realistic advice.

My "Lousy" comment was directed at me.

 

[java230]

Re: Prop Selection- Now with Tach!

Ok went for a solo WOT run on a glass lake. Hit 24.3, tach is an induction type and was bouncing all over.

Then went for a fully loaded trip. Cooler, 2 100lb dogs, wife daughter and niece. 9mph....at WOT about 3200 rpms.

9 pitch stoll the way to go?

 

[dazk14]

Re: Prop Selection- Now with Tach!

A 9" prop will rev through the roof. At 24 mph it would be turning in the neighborhood of 6300rpm. Rules of thumb go out the window when making large pitch changes.

Understand, as prop pitches drop, the percentage of pitch drops greater than it would on say a 19" pitch rig, thus 150/200rpm pitch change per inch tend to get exaggerated.

I am suggesting a 21% drop in pitch, which is quite a bit.

As I mentioned earlier, raising rpms into its designed powerband will produce more hp, again affecting the equation. Over-shooting the rpm mark will drop hp as well.

If you've called off the hunt with regard to the motor(which is fine), I'd suggest a Turning point Hustler 10-7/8" x 11"pitch. Cost from iboats incl hub kit is $98.24.

Lightly loaded you should pick up a few mph and not over rev the motor, while still having adequate load carrying capacity for the group you mentioned.

There are other props, but the combination of price and avoiding a large diameter change makes this my recommendation. Turning point makes good props.

Good luck!

 

[java230]

Re: Prop Selection- Now with Tach!

A 9" prop will rev through the roof. At 24 mph it would be turning in the neighborhood of 6300rpm. Rules of thumb go out the window when making large pitch changes.

Understand, as prop pitches drop, the percentage of pitch drops greater than it would on say a 19" pitch rig, thus 150/200rpm pitch change per inch tend to get exaggerated.

I am suggesting a 21% drop in pitch, which is quite a bit.

As I mentioned earlier, raising rpms into its designed powerband will produce more hp, again affecting the equation. Over-shooting the rpm mark will drop hp as well.

If you've called off the hunt with regard to the motor(which is fine), I'd suggest a Turning point Hustler 10-7/8" x 11"pitch. Cost from iboats incl hub kit is $98.24.

Lightly loaded you should pick up a few mph and not over rev the motor, while still having adequate load carrying capacity for the group you mentioned.

There are other props, but the combination of price and avoiding a large diameter change makes this my recommendation. Turning point makes good props.

Good luck!

dazk,
Thanks for the help. I'm not ruling out the motor, but I don't have any budget for a big rebuild or anything like that. Cleaning the carb if needed sure, new plugs, sure. But nothing major.

Ill see if i can find a local place that has a "test" program for props, seems like it would be good rather than shooting a shot in the dark.

I will normally have at least the wife and kid wit m so propping for that load sounds like the best bet.

Any idea of what the stock prop should have been on this motor/boat combo?

Again I REALLY appreciate the help. Im a boat newbie with an old boat....

 

[java230]

Re: Prop Selection- Now with Tach!

Ok i drilled a hole, back where there was cracked glass under the gas tank. Its almost all the way to the stern and about as close to the keel as i can get there.

And i found damp foam..... No standing water or anything, but it was definitely not bone dry. Probably the last 1/4" was damp.....


I will have to get a better weight on this thing and see how much water is in there.
Hopefully not much.




Back to props, how does this one look? 11" pitch, 11 5/8" diameter.

http://boatpropellers.iboats.com/Me...992603_Propeller/264/36258/?*******=472636549

 

[dazk14]

Re: Prop Selection- Now with Tach!

Ok i drilled a hole, back where there was cracked glass under the gas tank. Its almost all the way to the stern and about as close to the keel as i can get there.

And i found damp foam..... No standing water or anything, but it was definitely not bone dry. Probably the last 1/4" was damp.....


I will have to get a better weight on this thing and see how much water is in there.
Hopefully not much.

Back to props, how does this one look? 11" pitch, 11 5/8" diameter.

Michigan Wheel Vortex XHS Aluminum Boat Propeller #992603 for Mercury 40 HP Outboard 1977 & Newer 2-Stroke, Includes Model 402 - iboats

I can't picture what you found for wet foam...

However, don't get overly excited about finding wet foam. It is not a death sentence. FAR more often than not, it's like managing an aging body...Adjust your expectations, work with what you have, and enjoy!

I can't tell you how many 2+ year old boats - while drilling the 9/64" holes into the transom to install trim tabs - put out a solid stream of water...

And create great memories for many,many years. To shut up the Alarmists... Sure, check your transom for plainly obvious stress cracks that appear to be getting worse.

Sadly, we've cut up a LOT of boats, so i can speak of their structural condition - at their demise. Engine failure, rotted floors, bad vinyl interiors brought them in. Occasionally, a scary transom. Your boat style is a rarity.

To answer your specific question. A 14" prop is what we would have installed when new absent of anything unusual.

Quickly scanning this long thread, it appears you've educated yourself, have a handle on slip and the inherit uncertainty of making fairly large pitch changes, never mind diameter changes. No one can take the risk out of low priced prop selection.

The popularity of heavy 4 strokes has tended to push blade area/diameter up in the available selections. Turning point does offer an exchange program, but it isn't free. You ship + $25 and the prop must not be marked in any way. TP props can sometimes be "off" pitch wise from expected.

Steelespike may have a database on file, maybe he'll weigh in with a suggestion.

Hope that helps.

 

[java230]

Re: Prop Selection- Now with Tach!

I can't picture what you found for wet foam...

However, don't get overly excited about finding wet foam. It is not a death sentence. FAR more often than not, it's like managing an aging body...Adjust your expectations, work with what you have, and enjoy!

I can't tell you how many 2+ year old boats - while drilling the 9/64" holes into the transom to install trim tabs - put out a solid stream of water...

And create great memories for many,many years. To shut up the Alarmists... Sure, check your transom for plainly obvious stress cracks that appear to be getting worse.

Sadly, we've cut up a LOT of boats, so i can speak of their structural condition - at their demise. Engine failure, rotted floors, bad vinyl interiors brought them in. Occasionally, a scary transom. Your boat style is a rarity.

To answer your specific question. A 14" prop is what we would have installed when new absent of anything unusual.

Quickly scanning this long thread, it appears you've educated yourself, have a handle on slip and the inherit uncertainty of making fairly large pitch changes, never mind diameter changes. No one can take the risk out of low priced prop selection.

The popularity of heavy 4 strokes has tended to push blade area/diameter up in the available selections. Turning point does offer an exchange program, but it isn't free. You ship + $25 and the prop must not be marked in any way. TP props can sometimes be "off" pitch wise from expected.

Steelespike may have a database on file, maybe he'll weigh in with a suggestion.

Hope that helps.

Thanks I do appreciate the help. I'm coming from a 12 aluminum boat with a 7.5hp. It barely moved when loaded. I found a bit of wet foam, bottom 1/4" in a 3" deep section seemed wet. Won't know for sure without getting a good weight.

I'm totally fine with having an older boat that doesn't preform like a new one, it's not. I went out again tonight, enjoyed myself and did 21.5 the whole way. So would you still suggest a 11 pitch larger diameter? There is a 10" 12 pitch ss one on CL locally for $65.

 

[dazk14]

Re: Prop Selection- Now with Tach!

Thanks I do appreciate the help. I'm coming from a 12 aluminum boat with a 7.5hp. It barely moved when loaded. I found a bit of wet foam, bottom 1/4" in a 3" deep section seemed wet. Won't know for sure without getting a good weight.

I'm totally fine with having an older boat that doesn't preform like a new one, it's not. I went out again tonight, enjoyed myself and did 21.5 the whole way. So would you still suggest a 11 pitch larger diameter? There is a 10" 12 pitch ss one on CL locally for $65.

BUY IT!!!

Of course, see if he'll take a tad less...When you're actually there.

 

[java230]

Re: Prop Selection- Now with Tach!

BUY IT!!!

Of course, see if he'll take a tad less...When you're actually there.

Unfortunately it's an hour plus away! But I'm trying. I can't find much info on it but it appears to be a cabelas brand 10 or 10 1/2" 12 pitch

 

[java230]

Re: Prop Selection- Now with Tach!

Ended up having to drive 3 hours south for work, so i picked up the prop on the way.

Not sure how well it will work, But for $50 it's work a try. Stainless 10" 12" pitch. It's a cabelas brand and appears to have a solid brass hub.

 

[dazk14]

Re: Prop Selection- Now with Tach!

Ended up having to drive 3 hours south for work, so i picked up the prop on the way.

Not sure how well it will work, But for $50 it's work a try. Stainless 10" 12" pitch. It's a cabelas brand and appears to have a solid brass hub.

You can't get hurt with that deal. Worse case, double your money on Ebay.

Knowing the motor spent much of its life plowing through the water a low speeds at the sailing club, a good de-carb would be prudent.

That Prop should have very good anti-ventilation properties. If you have the opportunity, try a very light load with the motor trimmed out to the furthest hole that doesn't blow out. You may have to work the throttle a bit to settle the porpoising, and keep the prop connected.

 

[java230]

Re: Prop Selection- Now with Tach!

You can't get hurt with that deal. Worse case, double your money on Ebay.

Knowing the motor spent much of its life plowing through the water a low speeds at the sailing club, a good de-carb would be prudent.

That Prop should have very good anti-ventilation properties. If you have the opportunity, try a very light load with the motor trimmed out to the furthest hole that doesn't blow out. You may have to work the throttle a bit to settle the porpoising, and keep the prop connected.

I was thinking about a rebuild on the carb. It's been done before at some point, you can see the paint pen marks made on the adjustment screws

 

[java230]

Re: Prop Selection- Now with Tach!

Ran a can of sea foam through the engine. Smoked like crazy so it was probably pretty dirty.

Went out today with the new prop. Much better. With the three of us on board, it hit 25.5 in mild chop. Hole shot was way better too, under 5 seconds to plane.

With the stainless 10" 12" pitch, we did 25.5 at WOT and about 4800 RPM's.

 

[dazk14]

Re: Prop Selection- Now with Tach!

Close enough...I'm genuinely excited for you - neat little prop for $50 bucks. Sounds like you've got a nice little family and a great attitude.

Obviously, you'll need to do the niece and Bowser test. If you run a bit under 4500 WOT, that's still livable. Just don't run it full throttle for extended periods of time under those conditions.

However... The forum/future Search'ers would like some "lightest"(just you) loaded test data. GPS/Rpm at your normal running angle and same for exaggerated trim angle.

Fair enough?