posted 05-04-2008 11:43 AM ET (US)            

Vent holes allow some exhaust gases to escape the propeller hub at slow speeds and allow the propeller to ventilate a little bit and spin faster at a given boat speed than they would normally. This can be advantageous to boats that struggle to get on plane or boats where a fast hole shot is of the utmost importance.

posted 05-05-2008 07:44 PM ET (US)         

Although you have quite a bit more power than my 1988 2 liter 150, I would expect similar results from props.

I ran that identical 19" Vensura prop for a while, and finally sold it. I would not recommend it, except for strong mid range cruising. They are for deep V boats with a lower HP to weight ratio, where good acceleration is needed and lots of bow lift. It was consistantly 2 mph slower than the Laser II, and did not hold as well. To run it on the Rite Hite, I had to drop the engine down 3/4" for the same holding that the Laser II gave up higher. Laser II also gives the boat a MUCH smoother ride.

I also tried a Rev 4 which ran & held well, as fast as the Laser II, but these are not recommended for a shallow V lightweight boat like your Whaler, which clearly do not need stern lift as they skim over the water. An Enertia also gave me fabulous performance and would also be highly recommended by me.

Also recommend you go to Merc's Prop caculator. When used correctly, it's a fantastic tool and very accurate. Use the functions where you put in all the weights, based on your previous performance indications. Once dialed in, you can then backtrack and see what ANY HP Merc will give you on the rig, and look at all the prop recommendations of the various designs, based on your choice of performance objectives. It's very interesting to see the differences (such as usually they recommend a higher pitch prop for mid-range cruising, topping out at the very bottom of the RPM range). For the ribside 21, or any of the "banana" series boats, use "fiberglass fishing" as your boat category.

For the exact reason of cruising ecomony, I use a 21" Laser II with large vent plugs on mine, and top RPM of 5000 (2.0 gear ratio). Gives me 47 MPH top end. With your rig, I would guess the Opti 150 to give you 52 MPH, running a 19" Laser II right up to 5500.

My bottom line rec for a prop on the Optimax 150: a Laser II or Enertia.

Tbirdsey if you're reading this, same would apply to you, but with more pitch. Either a 21" or 23" Laser II, or maybe a 22" enertia. That boat is going to be fast.

posted 05-05-2008 09:50 PM ET (US)         

1. The Rite-Hite bracket is installed with the top hole's centerline down 1-1/8" from the top of the transom. See here:

http://smg.photobucket.com/albums/v429/lgoltz/Outrage%2021/?action=view& current=DSCN1361.jpg
This is so the bottom holes on the standard BIA bolt pattern in the bracket will come into the narrow inside transom space below the hatch, to receive the nuts. (top bolts have the nut on the outside) As you know this boat's somehwat shallow transom was designed before the advent of the BIA standard bolt pattern, and this mounting height allows it to work. No problems with the transom because of this.

2. The engine is mounted in the second set of holes to the bracket, one down from the lowest possible.

3. The bracket is then raised about 1". Mine is an 8" setback.

Altogether, I would say the anti-vent plate is running about 1-1/2" above the water flowing past it. That's about as high as it makes sense to go for a boat that only runs high forties. Any more height would not gain top end speed.

I'm very impressed with the fuel economy of the 150 Optimax. No wonder the magazines say they are the fuel economy champions of outboards. My 2 liter 150 2-stroke gets 3 MPG at 30 MPH cruise, so you are getting TWICE the fuel economy I am. A while back, someone here doubted that an Optimax could get 50% better fuel economy than a carb 2-stroke, on same hull. You are getting 100% better. Pretty impressive.

posted 05-06-2008 08:23 AM ET (US)            

Tom Clark & LHG pretty much summed it up. Here's the Mercury website that explains the PVS system in detail.
http://sites.mercurymarine.com/portal/page?_pageid=126,48572,126_49275& _dad=portal&_schema=portal

I have 17 P Revolution 4's on my older 285 Conquest with 225 Mercury 4 strokes. My boat had the solid plugs when I purchased it used about 2.5 years ago. The older CQ's with the notched hull in the stern were known as slow planing hulls and the hull was redesigned in later models.

posted 05-06-2008 02:19 PM ET (US)         

Brian, on my 25 Outrage with twin 200 EFI's, I run 21" Rev 4 props with the large vent plugs installed. This produced a tremendous increase in acceleration from the original solid plugs. No slippage at all.

posted 05-15-2008 09:58 AM ET (US)            

Thanks for reporting back. I'm glad that 19" Offshore is working so well for you.

Jim's experience demonstrates once again how vents on propellers are really not applicable to most Boston Whalers. In general I recommend plugging all vent holes; they are just not needed and may be detrimental to the boat's performance.

posted 05-15-2008 02:39 PM ET (US)         

I've got a whole pile of removed solid vent plugs. If you need some more, I'll drop them in the mail to you.

I ran the Vensura on my ribside with solid plugs also. On yours, with the tremendous acceleration of an Optimax fuel injection system, combined with the fast acceleration of the Vensura, solid vents would be all you need. The Laser II, on the other hand, is a slow accelerating prop, which is why Mercury sends them from the factory with medium plugs installed. Try the large size on that prop.