I/O vented holed props or not????

[AngelC]

Hey fellows.......I recently swaped out my damaged 3 blade aluminum 19pX14.5 prop with an exact size turning point legacy, but this one had vented holes. I have a 20ft boat with a 5.0GL I/O SX drive 220hp. I was happy with the prop that came with the boat when I bought it all except for at of hole and my base line was 4600 rpm WOT and 48 mph with full load and then I added trim tabs, out of whole is excellent now but the rest of perfomance is horrible. WOT with new 19pX 14-1/4 turning point Legacy is 4100rpm at 46mph with just my son and I. My average load is usually 7 people. My engine is rated at 4400 to 4800rpm so I am now under reving at 4100rpm. My question to you fellows is could it be that the vented holes on the prop have anything to do with this decreae of rpm's? or could it be the cupping of the new props? I read recently that vented hole props worked well on outboard but caused cavitaion and blow outs on I/O but not before going ahead and buying a 17p exact diameter Legacy vented that I have not tested yet. I know I will increase Rpm by 300 to 400 going from a 19p to 17p but the question is will I stll be under perfoming with these vented holed props on an I/O? I was thinking maybe just trying out a 18P 4 blade non-vented aluminuim prop and maybe hoping for better results. I realize this is all trial and error but I'm doing something wrong cuz it's starting to cost more and more. I just want the opinions from you experts because apparently I'm just spending more and more money and not acheiving any better results. Any help would be much appreciated.

Thank you,

 

[Tail_Gunner]

Re: I/O vented holed props or not????

Stilletto bay pro11 18"...something crazy is going on with that turning point. Like this response or not a 2cyl motor can or will create a bubble around the blades...a 4cycle ..naww.

Ok marble eye's could you plz make a apperance...

 

[lrdchaos]

Re: I/O vented holed props or not????

I was looking into the vent holes recently, and found that if your motor doesn't exhaust out of the lower unit the holes make no difference. I bet your motor exhaust comes out of the transom, so the vent holes are not your problem.

 

[AngelC]

Re: I/O vented holed props or not????

lrdchaos.....Thanks for the response. So by having the holes it would not effect the perfomance. When I had the non-vented prop it made a big diffrence and it was the same exact size as the vented. The only diffrence was the cupping and the holes. I know the cupping would have an effect but that much of one.

 

[Dhadley]

Re: I/O vented holed props or not????

As long as the exhaust goes thru the drive the holes will make a difference at lower sppeds, especially holeshot. If you have thru transom exhaust the holes won't make any difference. Once the rpms come up a little and the boat is on plane the holes won't make any difference. Your main issue is that you went from a prop with less bite to ine with more, even though they are the same pitch. That would be (most likely) OK on an outboard since you could raise the motor to take advantage of the better bite. Raising the drive & motor probably isn't going to happen with an I/O.

 

[AngelC]

Re: I/O vented holed props or not????

Dhadley......Thanks for the info, that is very helpful. What would you recommend for my boat. I have already bought the 17p which would raise the rpm's in the range I need to be. I'm at 4100rpm WOT now. So I would hopefully be at around 4500 going from a 19p to 17p, my boat is rated at 4400 to 4800 rpm, or should I look into a 18p 4 blade aluminum. I use the boat for water sports and cruising the lakes only. What do you think I would get the best performace for my boat with. Although, the 18p 4 blade would probably be a gamble to. I just want to try and narrow it down and not waste any more money.

Thanks for you help,
I really appreciate it.

 

[Dhadley]

Re: I/O vented holed props or not????

Since we're limited on the X dimension (height) adjustment the only variable we have is props. You're headed in the right direction - trying the same make & model in a different pitch. Going back to a 4 blade aluinum throws another unknown into the mix. Since you already have the 17 coming (or have it in hand) I'd give it a shot. At least you'll be comparing apples to apples although one is slightly bigger.....

 

[AngelC]

Re: I/O vented holed props or not????

Dhadley......THANK YOU, that's exactly what I was looking for. I needed some direction, an answer. I think I've been fustrated and feeling like I'm just throwing money away. Your right, I already have the 17p so I might as well give it a try. If that don't work out then I'll look into a 4 blade like you said apples to oranges.

Thank you for your help

 

[Dhadley]

Re: I/O vented holed props or not????

The other thing is that with more testing with like props the better idea we have as to how your hull reacts to changes in pitch alone. While it won't be a direct comparison to 4 blade props we'll at least have more info.

 

[AngelC]

Re: I/O vented holed props or not????

very true.......great point

 

[nlain]

Re: I/O vented holed props or not????

Just for a little more info, my boat came with 14X23P prop, I wanted a Turning Point, I bought the 14 1/4X23P and put it on, at cruise rpm I gained 5 mph, wot dropped to 4400 from 4800, otherwise the prop performed great, I sent Turning Point an email, they answered back that very few 4.3L Alpha1 could turn that prop because it is so aggressive, they swapped it out for a 14 1/4X21 I paid for shipping both ways. Go ahead and do the things you have been advised but also contact Turning Point I feel sure they will swap out for you also.

 

[AngelC]

Re: I/O vented holed props or not????

Nlain......What were the results when you switched out to the 21p?? I do have the 17p but have not tested it out. I got poor rusults with the 19p so, I called turning point and they advised me to down size to the 17p. They did tell me that the 15p would not get me out of the hole and that the 17p should do great. I'm going to test it asap. I was just not sure about the vented props because I to lost 400rpm's with the same size prop as the original that gave me better perfomance minus the hole shot.

 

[nlain]

Re: I/O vented holed props or not????

My weekends keep getting messed up and I have been unable to get it wet so I do not know what the difference is. I will say that the cup on the TP is aggressive and the rake looks different to my Merc stock prop. As good as the 23 was except the loss of wot by 400rpm I feel that the 21 will be good. The vent holes in the prop are supposed the let air bubbles build around the blades so the rpm will build faster therefore getting out of the hole quicker and at high rpm they should have no effect since the prop is spinning to fast for exhaust gas to pass thru the vent holes. Hope to try mine this weekend.

 

[AngelC]

Re: I/O vented holed props or not????

nlain....Thanks for that info, I as well haven't been able to get my boat to the water. If you do try yours out this weekend, can you let me know how your results came out. I'm really curious and hoping that it's nothing but positive. By the way.....saw your pics of your boat, very nice!!

 

[nlain]

Re: I/O vented holed props or not????

If I get to run this weekend I will post the results here and thanks for the remark on the pics.

 

[AngelC]

Re: I/O vented holed props or not????

Sounds good.......Thanks again

 

[a70eliminator]

Re: I/O vented holed props or not????

I just read your post and right away noticed you say, then I added trim tabs, did your old prop perform good with the tabs or did you add them afterwards along with your new prop?

 

[180shabah]

Re: I/O vented holed props or not????

I just read your post and right away noticed you say, then I added trim tabs, did your old prop perform good with the tabs or did you add them afterwards along with your new prop?

...And are they fully retracted for speed testing?

 

[AngelC]

Re: I/O vented holed props or not????

Hey guys.....I added the tabs after along with a new prop. The tabs are set in the center position and were their when I tested the new prop along with the tabs. But after doing some more reading, I just set them to the first hole which is setting #1 so now there fully retracted. Would the tabs have anything to do with the rpm drop?? I would think it would be the prop as the prop is like a gear. right?? What do you guys say?

 

[nlain]

Re: I/O vented holed props or not????

When I first ordered my Smart Tabs and installed them I had the 80lb actuators, I could not get the bow out of the water, I did not try wot but I do know that I used more throttle and sucked up a lot of gas that day. So the answer to the question is yes. Too much pressure on the tabs the bow will stay water buried in the water, more drag, less speed, less rpm, more gas. I can say that once adjust correctly to balance your boat that the Smart Tabs have done everything advertised for me.