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performance vent plugs

Not an easy question to answer as each has their opinions and wants, and they have their equipment and have their usage profile.

My first experience was with a Ranger bass boat what was not real stern heavy, but did have the fuel and batteries in the stern and dead rise and lifting strakes and a Pad, with the usual offset between the stern end of the pad and the transom. Besides fishing, I wanted to slalom ski behind it. I wanted enough RPM rise to get a fast hole shot with either situation. This was 1989 and my prop was the first Laser SS and I had it pitched for 6k RPM at WOT.....500 over the recommended upper limit with me alone in the boat. I think the ports were ⅜" and no plugs were available back then.

Hammering down in the hole I'd get about 1 RPM increase best I can remember which would drop, like shifting an old stick shift car into overdrive, by that amount....the way I figured the amount of RPM gain once I was on the water, coming up to speed with the new water sealing off the ports. I couldn't make a comparison between ports and plugged ports as plugs weren't available at the time and if I changed props that would invalidate any data.

My rule of thumb determined many years later on other props is you want a prop that will get you in the upper end of your recommended RPM range with your regular boat load and summer time temps. Then you want a hole diameter that will give you a reasonable (your determination) amount of RPM increase for a reasonably fast hole shot, but not too much which would slow down the transition. I'd say something like dropping the pitch 3-4" for the shot then returning to the WOT RPM choice once up and running type thing for a stern heavy application and less for less weight. Actual numbers depend on your desires, your rig, and your selected port size.

I'd start with the blank, get your data and start opening the hole till you like what you have. Neat thing about plugs is that you can swap them for the occasion.....the other thing about ports is that you can essentially make a 4 blade shallower pitched prop out of your existing prop when you are in the mood for "just over plane" cruising....soon as the slip stream water pressure drops below a certain level, the ports will open back up and increase your RPMS, dropping your speed and making your ability to hold that speed and attitude more precisely....like you could with the shallower pitched 4 blade.
 
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faztbullet said:
Depends on the boat...start off with all solid and work way up till find best holeshot with max load.
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the boat is a 2016 stratos 201xl with a 250 optimax the prop centerline is at 3 1/8 below the pad . It also has 2 10ft talons and a 36volt troling motor with all the batteries in the back and 3/4 tank of gas with 2 of the 4 plugs installed the prop lost bite in the hole shot [blow out] as its called . I will installed the other 2 plugs and re test . Thanks for all the help.
 
You are setting yourself up for vibrations and the blow out you experienced...possibly. You need to balance the load on the blades for smooth operation. Trim position is TBD, by trial and error. You on a jack plate? I think the pad is forward of the transom by what, 6"? You running a 14" diameter prop gives you 7" radius. With AV plate even with pad.....extended straight edge, the shaft would be 7" below. Allowing 1" for pad setback and 1" for jack plate would move shaft to 5" below pad. You at 3 ½" puts you at AV plate 1 ½" above hull if no pad setback and no jack plate were there which would be reasonable for a setup on a heavy stern boat with lots of HP to get it up and out like you have.....all just my playing with numbers.

Closest I came to your rig was a 17' Ranger with a Merc 115 Tower. It had the typical Ranger pad hull, little more dead rise than most Rangers at the stern, with setback, no jack plate, and I was running the engine 1 hole up on the transom...about 1"....so that's close to what you are currently running if you have a jack plate....otherwise you "may" be a tad high. I was running the original Laser SS, don't remember the hole size (didn't have plugs back then) and had enough trim such that I could trim up till it started loosing speed and increasing in RPMs....when running full out. Not an expert but I have some experience and have picked up a few things on boating sites like this one, here and there over the years. You could always drop the plate if needed (if you have one) to check out other positions.....but the big guns on here always prompted to get your setup up right, then play with the prop.....so, lets continue with what you have....make sense?

We (I) are assuming that you firewall the throttle for the shot....step function thing...0 to max. I think you need to do as We recommended: Plug with 4 solid plugs and make several runs trying different trim positions in the hole shot. Some blowing out isn't all that bad (to me) if it results in the engine getting the RPMs up fast and doesn't amount to all that much blowout, since once the boat gets moving, aided by some porpoising....helps, the bite will improve and speed increase rapidly. I have come out of the hole faster with the engine perpendicular to the line of the hull, vs tucked all the way in and I think it was because I could get some ventilation which aided in getting the RPMS up faster, getting my thrust up faster, the porpoising helped the engine rev and bite and rev and bite. You just have to play with the trim and see what works best.

Then start increasing the hole size from your small plug (if you have received them) testing as above on up thru the largest. Or if you have your Delrin plugs installed, drill out 5/16" in all 4 for the first run and move up to ⅜ if you aren't happy. By the time you get there you should have a handle on where you want to be.
 
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Yes i do have a jack plate it's a 6" atlas the numbers a gave before are with the plate set at 2" above the bottom so i can go up or down some. I will also try trimming up a bit before the holeshot. Thanks for all the help this bass boat stuff is new to me i have a lot to learn. Thanks again.
 
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