New boater: Ventilation(?) on 17P and 24P

[ddlaz]

Hey all. Just got my first 17' F/S boat with a 150 xr2. The previous owner had a 24 pitch 3 blade ss prop on the motor and it didnt seem right so I put on a 17 pitch 3 blade ss prop that he included. He says it was his 'hole shot' prop.

I have only been out a few times on the boat and would like to clarify some things before I overrev/overwork this motor.
With the 24 pitch prop I drive it the following way:
Trim down all the way, wot
the bow comes up and does not plane for a long time(seemingly, could actually be short, I have nothing to compare this with)
before the boat will get on plane, the rpms will rise rapidly at a point and you can hear the motor sound different like there's no load on it
At this point, I throttle down a bit to lower the bow and then throttle back up and it will sometimes get on plane, if not I trim up a tad to give it more push (attempting to get the prop parallel with the water surface)

Once on plane, everything is good and I trim up little by little until I get to where it doesn't want to pick up speed anymore. My speedo doesn't work currently, I tried blowing air into the hose and the speedo needle moved, blew air the other way and air came out of the pitot hole on the outboard fine. Another topic later. So, I don't know my speed but I try to cruise it at 5500 rpm.

I switched to the 17 pitch prop last night, started with trim down at wot and the boat went NOWHERE. It just seemed to bog down. Stayed at 1500-2000 rpm until I could pick up enough speed to get in the powerband of the motor. I tried trimming up a bit to get the prop parallel with the water surface but then I'd get the rapid rpm rise again at 3500 rpm with bow up high. I was testing this on a fairly small lake so I didn't get to a good cruising speed/rpm.

What am I doing wrong? Do I need to move my motor up/down a notch on the transom bracket? It is currently at the 2nd hole from the top. Start with trim at a different level?

 

[SkiDad]

Re: New boater: Ventilation(?) on 17P and 24P

sounds like something is wrong with the 17 pitch prop - maybe a spun hub ? or you have another issue. i would think that boat could easy run a 19 pitch at that much engine to size. I wonder if you should just pick up a new aluminum prop to get a starting point. If you have a smart phone you can download a free GPS app to get your speed for testing - or if you have a car GPS. What is your RPM showing at idle ? Just wonder if that tach is off too. Something is definitely not right - did you do a water test when you bought it ?

 

[ddlaz]

Re: New boater: Ventilation(?) on 17P and 24P

sounds like something is wrong with the 17 pitch prop - maybe a spun hub ? or you have another issue. i would think that boat could easy run a 19 pitch at that much engine to size. I wonder if you should just pick up a new aluminum prop to get a starting point. If you have a smart phone you can download a free GPS app to get your speed for testing - or if you have a car GPS. What is your RPM showing at idle ? Just wonder if that tach is off too. Something is definitely not right - did you do a water test when you bought it ?

Hmm. I never thought that the hub could be spun. I'll test it next time I'm out on the lake. Why do you suggest an aluminum prop and not ss or other?

I also did not even think of using my phone as a gps/speed app. I am always too concentrated on figuring out how to get on plane efficiently.


I did do a water test when I bought it. I let him drive it first and show me how to go about it. He mentioned that as the bow lifted up, the revs will climb quickly and he'll let off the throttle a bit and trimmed up a little then back to WOT. It worked when he was telling me but I must be forgetting something.

 

[SkiDad]

Re: New boater: Ventilation(?) on 17P and 24P

what is your goal for the boat - to go fast or to pull skiers ? that will make a difference in the prop advice.

the reason I said aluminum is b/c of cost - you can get something like a mercury black max prop at a local marina for under 150.00 - and you don't have a lot of cash involved. Once you get the right pitch for your boat then you can look at SS. Keep the aluminum for a spare and sell your other 2 props on craigslist or something. Well, this is coming from a guy with a very limited boating cash, so I don't have a big budget myself.

for reference, before I got my boat, I was test driving a 17' checkmate with a 135 black max on it - it had a 21 pitch stainless - it had no problem planing and we had 750 lbs of people in the boat. I think it ran a hair over 5000 rpm / high 40's mph. They said they skied with it for slalom but I would have put a 19 on it for skiing as it took about 6 or 7 seconds to plane.

my boat will plane in 4 seconds or less and I think that 3-4 seconds is normal you should be looking for. And I don't think you should have to trim down to take off - yes it will plane a little faster but shouldn't be necessary. I apologize if you know these things, not sure if you had a boat before.

maybe the guy who had the boat was strictly interested in going fast and the motor is too high. I hear the rule of thump is anti-cavitation plate is level with the bottom of the boat or 1 inch above. Mine is 1" below, i would raise mine an inch but my engine is not that adjustable without re-drilling.

 

[MaPaHa]

Re: New boater: Ventilation(?) on 17P and 24P

I’m not sure what to think about switching to the 17 prop and bogging down and not revving up. That one should have taken off quickly. That’s puzzling.

I’ve had a 18.9 F/S with a 175 for 17 years since new and it was set up to run fast from the dealer. It would hit 70 plus mph but would not come out of the hole nor pull a skier and when you hooked a tube behind it wanted to fall back off plane with the nose in the air. And yes, the bow stuck up in the air for a while before getting on plane.

I talked to the dealer about my disappointment and they swapped the prop to a 4 blade with exhaust ports in it and it wasn’t the same boat after that. It jumped out on plane and the stern gained a lot of lift at lower speeds and it’s great for tubing and skiing. I might have lost 2-3 mph but at 70 + I didn’t mind.

Exhaust ports in a prop will allow the motor to spin up on take off but I don’t think that’s what your’s is doing. I believe the motor is set one notch too high for the prop you have and it’s ventilating. If you stick with that prop, I would try lowering the motor one notch but you may lose a bit on top end. However, if you change to a 4 blade I wouldn’t move the motor until you try it. They often times get a better bite and have less ventilation.

I run a 4 blade on this F/S boat along with my tri-toon with a 150 hp and personally, unless I was setting up a boat to run all out, I wouldn’t use a 3 blade. 4 blades are generally made for hole shot thru mid to upper range and especially for boats that are stern heavy.

Mitzys question about what are your goals for the boat is the best question you have to ask yourself. Consider that the previous owner seemed to know boats fairly well and for him to tolerate the motor ventilating as it breaks over on plane (if that’s what’s happening), makes me think the boat was set up to run flat out possibility with a lighter load and he was willing to put up with getting out of the hole. Maybe the motor was set high to improve top speed. I’m guessing that 24 pitch prop is a high rake prop that’s made to run with part of the blade out of the water on top end for all out speed. You may want to put the family in the boat and pull tubers, skiers and cruise the lake at 3,700 – 4,000 rpm which is another set up.

I’ve done a fair amount of speculation here but having a boat similar I understand how they run. They are fairly butt heavy at low to medium speed but run like a striped ape at high speed. If you want to change the performance at mid range speed and get the butt out of the water quicker without too much loss at high speed then go with a 4 blade prop. I like the guys at Power Tech Props because they will help you get the right prop and refer you to their dealer network so you can choose one near you to order it.

I’ve found most dealers aren’t very helpful in selecting the right prop. I would rather deal with a good prop shop or manufacturer. If they don’t run a prop calculation with you’re motor’s gear box ratio then I would look for another shop.

 

[ddlaz]

Re: New boater: Ventilation(?) on 17P and 24P

what is your goal for the boat - to go fast or to pull skiers ? that will make a difference in the prop advice.

the reason I said aluminum is b/c of cost - you can get something like a mercury black max prop at a local marina for under 150.00 - and you don't have a lot of cash involved. Once you get the right pitch for your boat then you can look at SS. Keep the aluminum for a spare and sell your other 2 props on craigslist or something. Well, this is coming from a guy with a very limited boating cash, so I don't have a big budget myself.

for reference, before I got my boat, I was test driving a 17' checkmate with a 135 black max on it - it had a 21 pitch stainless - it had no problem planing and we had 750 lbs of people in the boat. I think it ran a hair over 5000 rpm / high 40's mph. They said they skied with it for slalom but I would have put a 19 on it for skiing as it took about 6 or 7 seconds to plane.

my boat will plane in 4 seconds or less and I think that 3-4 seconds is normal you should be looking for. And I don't think you should have to trim down to take off - yes it will plane a little faster but shouldn't be necessary. I apologize if you know these things, not sure if you had a boat before.

I don't care too much about speed or skiing to be honest, I just want to get to my fishing spot(s) and troll. Fast is a luxury, as well as skiing/tubing.

I understand on the alum prop deal. I just can't imagine why he had a 24 pitch prop and a 17. very opposite spectrums. The idle is at 900'ish btw.

 

[ddlaz]

Re: New boater: Ventilation(?) on 17P and 24P

I?m not sure what to think about switching to the 17 prop and bogging down and not revving up. That one should have taken off quickly. That?s puzzling.

I agree, puzzling. I thought for sure a lower pitch would shoot me off. It wouldn't even rev up. From what I've read, whether it's a spun hub or not, it should definitely rev with or without acceleration.

I?ve had a 18.9 F/S with a 175 for 17 years since new and it was set up to run fast from the dealer. It would hit 70 plus mph but would not come out of the hole nor pull a skier and when you hooked a tube behind it wanted to fall back off plane with the nose in the air. And yes, the bow stuck up in the air for a while before getting on plane.

I talked to the dealer about my disappointment and they swapped the prop to a 4 blade with exhaust ports in it and it wasn?t the same boat after that. It jumped out on plane and the stern gained a lot of lift at lower speeds and it?s great for tubing and skiing. I might have lost 2-3 mph but at 70 + I didn?t mind.

Exhaust ports in a prop will allow the motor to spin up on take off but I don?t think that?s what your?s is doing. I believe the motor is set one notch too high for the prop you have and it?s ventilating. If you stick with that prop, I would try lowering the motor one notch but you may lose a bit on top end. However, if you change to a 4 blade I wouldn?t move the motor until you try it. They often times get a better bite and have less ventilation.

I run a 4 blade on this F/S boat along with my tri-toon with a 150 hp and personally, unless I was setting up a boat to run all out, I wouldn?t use a 3 blade. 4 blades are generally made for hole shot thru mid to upper range and especially for boats that are stern heavy.

Mitzys question about what are your goals for the boat is the best question you have to ask yourself. Consider that the previous owner seemed to know boats fairly well and for him to tolerate the motor ventilating as it breaks over on plane (if that?s what?s happening), makes me think the boat was set up to run flat out possibility with a lighter load and he was willing to put up with getting out of the hole. Maybe the motor was set high to improve top speed. I?m guessing that 24 pitch prop is a high rake prop that?s made to run with part of the blade out of the water on top end for all out speed. You may want to put the family in the boat and pull tubers, skiers and cruise the lake at 3,700 ? 4,000 rpm which is another set up.

Good information. He told me the 17 prop would get out of the hole quickly, it was his 'hot rod' prop. It did the opposite. I would assume that just swapping props would get the same result that he is talking of.

I marked the hub and prop and I'm taking it out on a bigger lake tomorrow so we'll see if the hub is spun on the 17 pitch. I see slight gaps like the hub or prop has some ovality to it, maybe it is spun, who knows.

Thanks for the info guys. I might find a prop shop and talk to them a bit more, maybe they'd like to take the boat out and show me what I'm doing wrong too. Although fearful they might want to sandbag it and sell me a prop.

 

[Texasmark]

Re: New boater: Ventilation(?) on 17P and 24P

The proper prop for your rig is one that will allow your engine to run at the upper end of the recommended rpm range at WOT with the load/under the conditions, you normally run.....period!

If you use water toys, you really need to prop for them as stated above and when not in use just back off the throttle to keep the rpms in check.

The difference in a 17 and 24P prop is HUMONGOUS!!!!!!! Don't expect similarities out of their performance. As a matter of fact I have a Ballistic SS 17P, 21P and 24P for my current boat. Difference as one would expect: The 17 will give you whiplash out of the hole but will redline at like 25 mph. The 21 is pretty snappy out of the hole and I can goose the engine and get immediate boat response, like a hot rod. I also can run it to 6500 rpm on a 5500 rpm rated engine. I don't do it normally, but as a matter of record, I just ran it up one day to see what the max rpms and speed were. Turns out I can run about the same top end mph with it as the 24 but obviously at a higher rpm.

The 24 takes some time in the hole as one would expect as it is a lot of pitch for a 90 horse engine on a 17' boat. So to solve that I ported it which I will discuss later. Once up the 24 will run me about 50 mph at around 5700 rpm. Good place to be as my engine is rated for 5500 but now I have this girlfriend that likes me to take her boating and she likes the rum rum which the 21 gives me so I am using it now and just holding the throttle back, like I mentioned to you above, to keep the rpms within limits and not running WOT. I run about 42 there which is fine. Can't tell the difference between 42 and 50 anyway.
--------
Some props have ports just behind and under the leading edge of the blades. The ports are designed to allow exhaust gasses to flow over the blades, reducing the density of the water and allowing the engine to run "unloaded". This allows the engine to get it's rpms much faster and allows for a faster hole shot. At speed they naturally seal off and you don't know they're there.

If the hole is too small it is useless. If too large you will never get out of the hole.....there are the limits. You size the hole such that you gain several hundred rpms in the initial hole which you keep (2-300 over what you would have otherwise at a specific point in the plane out process....obviously rpms increase as the boat speed increases.) till you get on plane and start building speed where the holes seal off, the engine drops down in rpms with the new load of all water and away your go.....to me it's like back in the old days when you had a stick shift car with overdrive. When you let off the accelerator and it dropped into OD and you put your foot back on the gas the engine was running at a lower rpm.

On your hole problem with excessive rpms, you have one of 4 things: 1. You have a ported prop and the holes are too large. 2. Your engine is set too high and is ventilating....sucking in air from just above the prop.....a whale's tail can help to prevent that, 3. Something wrong with your setup between the boat and the water that is supposed to be in front of the prop for it to operate. 4. Something wrong with your props.

HTH,
Mark

 

[jestor68]

Re: New boater: Ventilation(?) on 17P and 24P

Check your pad to prop shaft measurement(start at 3.5" below the pad). It sounds like it's too high since you're getting excessive ventilation. You shouldn't have to juggle the throttle in order to get it to plane off; IF the motor height is right.

Folks love to set it too high for max speed, and screw up the boats over all performance.

 

[ddlaz]

Re: New boater: Ventilation(?) on 17P and 24P

The proper prop for your rig is one that will allow your engine to run at the upper end of the recommended rpm range at WOT with the load/under the conditions, you normally run.....period!

If you use water toys, you really need to prop for them as stated above and when not in use just back off the throttle to keep the rpms in check.

The difference in a 17 and 24P prop is HUMONGOUS!!!!!!! Don't expect similarities out of their performance. As a matter of fact I have a Ballistic SS 17P, 21P and 24P for my current boat. Difference as one would expect: The 17 will give you whiplash out of the hole but will redline at like 25 mph. The 21 is pretty snappy out of the hole and I can goose the engine and get immediate boat response, like a hot rod. I also can run it to 6500 rpm on a 5500 rpm rated engine. I don't do it normally, but as a matter of record, I just ran it up one day to see what the max rpms and speed were. Turns out I can run about the same top end mph with it as the 24 but obviously at a higher rpm.

The 24 takes some time in the hole as one would expect as it is a lot of pitch for a 90 horse engine on a 17' boat. So to solve that I ported it which I will discuss later. Once up the 24 will run me about 50 mph at around 5700 rpm. Good place to be as my engine is rated for 5500 but now I have this girlfriend that likes me to take her boating and she likes the rum rum which the 21 gives me so I am using it now and just holding the throttle back, like I mentioned to you above, to keep the rpms within limits and not running WOT. I run about 42 there which is fine. Can't tell the difference between 42 and 50 anyway.
--------
Some props have ports just behind and under the leading edge of the blades. The ports are designed to allow exhaust gasses to flow over the blades, reducing the density of the water and allowing the engine to run "unloaded". This allows the engine to get it's rpms much faster and allows for a faster hole shot. At speed they naturally seal off and you don't know they're there.

If the hole is too small it is useless. If too large you will never get out of the hole.....there are the limits. You size the hole such that you gain several hundred rpms in the initial hole which you keep (2-300 over what you would have otherwise at a specific point in the plane out process....obviously rpms increase as the boat speed increases.) till you get on plane and start building speed where the holes seal off, the engine drops down in rpms with the new load of all water and away your go.....to me it's like back in the old days when you had a stick shift car with overdrive. When you let off the accelerator and it dropped into OD and you put your foot back on the gas the engine was running at a lower rpm.

On your hole problem with excessive rpms, you have one of 4 things: 1. You have a ported prop and the holes are too large. 2. Your engine is set too high and is ventilating....sucking in air from just above the prop.....a whale's tail can help to prevent that, 3. Something wrong with your setup between the boat and the water that is supposed to be in front of the prop for it to operate. 4. Something wrong with your props.

HTH,
Mark

Hmm.. I replied last night but i guess I didn't post it. I'll measure my pad to shaft distances and adjust accordingly. The props have three holes that when mounted, are located towards the bow, are these the ports you're talking about? If so, they don't look modified at all.

 

[Texasmark]

Re: New boater: Ventilation(?) on 17P and 24P

Gimme a picture of the side of the prop just under the leading edge of the blade and I'll tell you.

Mark

 

[ddlaz]

Re: New boater: Ventilation(?) on 17P and 24P

Gimme a picture of the side of the prop just under the leading edge of the blade and I'll tell you.

Mark

No need for a picture, I compared both of the props and the 17p has no ports and the 24p does.
I switched back to the 24p and it takes about 5 secs to get on plane, 6k rpm gets me to about 58 mph (phone gps). I limit it to 5500 just to be safe.

Maybe I'm just used to driving it now, but with the 24p prop, I go wot with outboard trimmed down all the way and it'll jump up and motor will sound like there's little to no load on it and jump to 6k rpm for a few seconds until it picks up enough speed to get on plane. Once on plane, the motor sounds good again and rpms drop to around 3500 rpms, building up to 6k as mentioned before.

 

[Texasmark]

Re: New boater: Ventilation(?) on 17P and 24P

You are experiencing the effects of the porting and that's exactly why they are in the prop. You get the great hole shot and the great top end. Sounds like you are there.

I never trim all the way down on hole shot and do just what you said. As I'm picking up speed, I am trimmed out too far vs initial speed (cause of porpoising, but doing it deliberately) and the boat porpoises a little. Every time it does it revs and when it bites it bites harder as everything is picking up speed including the engine upping the rpms which is upping the usable hp. and the take off is really fast and fun.

Mark