BGIII

iTrader: (3)

I'd take more (reliable) horsepower or higher Bravo drives any day, even if they both got me to the same top speed. My frame of reference is what I would call performance pleasure boating, not racing. If I had a step bottom boat, I may have a different opinion as I think those tend to respond better to high X-dimensions.

There is a reason they are always for sale on these sites. The same ones are probably being passed around like a Fountain skank.

carcrazy167

BenPerfected, I have heard through the grapevine about all the work you have done in rigging your Scarab. I have a lot of respect for that kind of perseverance. I too, am one of those fools to far exceed the value of my boat (same hull as yours). I'm very attached to my Scarab; have had it for 20 years and foresee many more to come. I would be very curious too hear what you have found to be the fastest set up for our 30 foot Scarab hull. Particularly: what was the prop shaft relation to the bottom of the boat and did extension boxes help in "high" x-dimension set ups on this hull? Also, can this old straight v-bottom hull plane without drama with a high "X". Planing quickly is important to me because I like to water ski behind my Scarab. My 540s dyno at 640HP, I'm running the TRS drives still in the stock location (prop shaft 8 inches below the bottom!) turning labbed (trimmed down) 28 pitch Bravo 4-blades. At 5600 RPM I see 83 MPH on GPS. Changing the drive height will be the next phase of work for me. It would be great to hear what set ups you found to work well.

endeavour32

iTrader: (4)

Thanks for all the input guys! I'm buying the shorty Sportmasters, soon I will see what raising the X does on a straight bottom Formula. Benperfected, it sounds like you have been through many stages in your project. When you first added the short drives, what was the effect on the props? I'm currently running Bravos, and I'm at least 400 rpms from where I really want to be at WOT rpm's. Did both rpms and slip increase with the addition of the shorty drives? When I work on the boat this weekend, I'm going to get some measurements and I'll report back.

class6

Find a set of Imco's not Sportmasters

endeavour32

iTrader: (4)

What what I've read, the only reason the IMCO is faster is because the skeg is longer on the Sportmaster. That is a pretty easy fix, I'll just trim the skeg to the same length as the IMCO. One of the members on here tested the Sportmaster and Imco's back to back and there was no speed advantage at all to either until over 100 mph. At which point the advantage went to the Sportmaster I believe.

Bawana

I have used both Imco & Sportmaster shorties with great results. The Imco has a longer case, and a bit more nose cone. I will add that the Imco IMO does need modification to the water inlet for a couple of reasons. First, water pressure, second cavitation.[ATTACH=CONFIG]551131[/ATTACH][ATTACH=CONFIG]551132[/ATTACH][ATTACH=CONFIG]551133[/ATTACH]
The pics are of the Imco, you can see the water pickup is long and sloppy, it also causes cavitation as you can see from the pic. It actually burned into the case, and what do you think that does to the props performance... not good. But The nice thing is it can be modified to fit your exact needs for water pressure as you can see what I do in the pic. Both drives have long skags that too can be cut down to fit your needs. Both Merc & Imco make the skags long to accommodate a very high X for cats. They cast the cases not knowing what application they will be used on. I cut different lengths off of both brands to fit there application. Usually 2 to 4 inches.
I don't think you can go wrong with either case, I will say, I think there is more used Imco's out there for sale, and if you decide to sell for whatever reason, the Merc's will bring more resale.
Will you see big speed increase? You don't know till you try. I will also add that every boat that I put shorties on, drove and handled better, that is if it worked out.

Bawana

One more thing if you have to adjust the Merc water pressure, you simply drill, tap and plug water inlets until you get you desired water pressure. So the Merc might be a better buy for you if you can find them reasonable. Also as stated by someone above, if you get used drives, have them inspected for wear.

rexcramer1

Congrats to you for taking the plunge, I am following this with great interest as a fellow straight bottom Formula owner. I run the same speeds as you, only difference is my hull has a notch at the transom. No one has really tested shorties thoroughly (several different props, etc) and documented it well.
I do need a lot of trim to hit top speed, usually about 6 on the indicators

endeavour32

iTrader: (4)

What kind of engines are you running rex? The 336 is very similar to the 311, which even though bigger, typically runs the same speed with the same power as the 292. I've got to run a lot of trim on my boat as well. The best prop I ran on mine was a Hydromotive QIV. The only reason I kept the bravos is Blades said he could make them out preform the hydros. I was going to ship them off to him to work on, but now with the shorties I don't want to do anything with the props until I know how this new set up is going to run.

BenPerfected

Do more searches, there has been extensive testing with the -2 Imco/Merc lowers and lots of info posted on OSO over the last 10+ years.