Ventilation Holes

[EEaton]

Hello all,<br /><br />I have a 2004 18’ Chaparral with the 3.0L and an Alpha 1 drive. This is about a 2100-pound boat. It came with a 14.25” x 21P prop. I have been very impressed with this prop so far. It has an excellent hole shot, and a fair top speed even with 4 adults and 3 children on board.<br /><br />Two weeks ago, we were on vacation and tapped some underwater rocks. We were able to finish out the week with this prop, with no real problems. On the way home I found a “deal” on a Quicksilver stainless prop of the same diameter and pitch. I was expecting better performance out of the stainless, but yesterday when we took it out for the first time since the new prop, I was really disappointed. The hole shot is destroyed, and top speed is also down about 4mph. WOT RPMS are also up a bit.<br /><br />I believe what is happening is that the new prop is ventilating. At least that is how it sounds and feels. This prop has rather large ventilation holes behind the blades. My aluminum prop didn’t have these. They are actually shaped kind of like elongated D’s, and are probably roughly 3/8” to 1/2” in diameter. They do appear to be factory holes, as in they don’t appear to have been added as an after thought.<br /><br />My questions are; do you guys think this could be my problem? And also is there something (maybe JB Weld) that I can use to plug these holes and try it out? I can easily get them welded in solid, but I thought I should try it temporarily first.<br /><br />Sorry for the lengthy post, but any ideas will be greatly appreciated.

 

[tommays]

Re: Ventilation Holes

it sounds like you have a prop with a PVS system (Performance Vent System) which should allow you to use plugs to block the vents or change size<br /><br /> http://www.boats.com/boat-articles/Engines-115/PVS+Propeller+Test/1855.html <br /><br /><br />

<br /><br /><br />i use a 14 x 19 prop with 1/4 inch vents on my 20 ft boat with a 3.0 and find that with a full load like that a 21 in prop is just to big for the motor <br /><br />you dont metion your WOT RPM but the motor should be able to run around 4600 to 4800 rpm with the correct prop <br /><br /><br />tommays

 

[EEaton]

Re: Ventilation Holes

Thanks for the reply tommays.<br /><br />It is a used prop, and about all I know is the size and pitch and that it is a Quicksilver prop. Do you know of any web page that has a picture of the plugs that the link mentioned?<br /><br />My WOT RPMs were around 4600 with the aluminum prop. With the stainless I am getting around 4800, but a slightly lower top speed. Of course I need to run it again with a few less people to be sure.

 

[hoot]

Re: Ventilation Holes

http://www.marinemechanic.com/site/mercury-prop-venting.htm <br /><br />have a look at this.

 

[EEaton]

Re: Ventilation Holes

Those plugs appear to go into a round hole. My prop has non-round holes. They are square on one end, and rounded on the other. Like a rectangle with one end rounded. Or if you took the letter 'D' and stretched it horizontally.

 

[EEaton]

Re: Ventilation Holes

Woops. Double post.

 

[EEaton]

Re: Ventilation Holes

Here is a pic of the prop. It is a Quicksilver prop. The numbers on it are "48 11070 A40 21P". You can see one of the ventilation holes at the base.<br /><br />

<br /><br />My question is, can I use something like JB Weld to fill in these holes and try it out? Or is there some better product to use?<br /><br />Obviously, I would be getting them welded in if filling them helps. I just want to be able to try it temporarily first.<br /><br />Any ideas?

 

[tommays]

Re: Ventilation Holes

its a quicksilver prop why not just call merc and get the facts on what can be done i would think you could get the plugs pretty easy unless they tell you its not a factory mod but a DIY job<br /><br />and those are some pretty big holes to weld i would really try to avoide that<br /><br />also that prop looks real close to the gear case do you have the correct thrust washer behind it ?<br /><br />tommays

 

[EEaton]

Re: Ventilation Holes

Call Merc. Hmm, now that isn't a bad idea. I'll give that a try and see what they say. I assume there is a number on their web page.<br /><br />As for the welding, I have a brother-in-law that welds jet turbines for a living, he assures me that welding them in is no problem. He has repaired and re-balanced a couple of aluminum props for me in the past and done a great job, so I guess I'll believe him. <br /><br />Of course I have to re-paint them myself.<br />

 

[EEaton]

Re: Ventilation Holes

Oh yeah. The thrust washer should be fine, it is straight from the prop shop for that prop. Same size as came with the boat. I think the picture is making it look closer, because I actually thought it was farther away than the aluminum prop was.

 

[John_S]

Re: Ventilation Holes

Eric,<br /><br />Just a thought. If Merc confirms it is a modified prop, such that the Merc plugs don't work, just go ahead and have it welded. Putting JB weld on it, might complicate the latter weld. If you want to expierment with venting latter, just do it the old way, drilling small holes. Given the size of the vent holes in the picture, I highly suspect that is the cause of your problems.

 

[EEaton]

Re: Ventilation Holes

Well, I called Merc. The official word is, here is a part number that might work. It says it supports part numbers with a suffix of A41 and A45. Mine is an A40.<br /><br />So, I guess I'll see if I can find a place to order them and give them a try. If they stay in long enough to confirm my Suspicions, it will be worth it.<br /><br />Anyone know of a good mail order Merc distributor?