Twin Promax 300 - how close?

Toffen · 06-10-2003, 06:08 PM

Hi!

I know I have been into this before, but pls help.

I have made some serious measurements, and I can get two Promax 300 on my Phantom 25 (its only 5,5 feet wide) if I mount them 21 - 21,5 inches senter to senter. This mean 1 - 1,5 inches between the cowlings. I can not wider due to the stringer system at the transom. Is this possible?

I also need to convert to 15 inches midsections, as the engines will be mounted direct on the transom. Is this possible to get hold of?

Its reccommended to rise the engine 6-8 inches with a twin installation according to Merc Hi Perf. Any ideas of propheight?

Cheeers, Toffen - Norway

06-10-2003, 10:19 PM

Toffen..your a crazy bastard....what a ride that will be..one guy to drive and one guy to scream. I recently moved my motors in closer trying to pic up a few MPH. They are Mercury Bridgeports mounted 17 7/8 center to center. about 1-1.5 inches between cowls..they actually rub a little on a full lock turn. I have a 24ft v-hull(Banana Boat Ltd) 7'10" beam.Ive only had it out once ..i had a low water pressure problem but i think it is due to the motors being too high. A guy from around my area who told me to move them in closer has run 17.5 centers without a problem. My boat had 22" centers originally with no problems. Good luck..if you put twin 300's on that hull your my hero!!!

mcollinstn · 06-10-2003, 11:13 PM

Toffen

I've actually seen several twin outboard raceboats with the motors mounted in a "V" with the props closer together than the powerheads. This might be your best solution since I'd guess your cowlings will rub on each other when you turn - might even rub so much to restrict the turning angle...

mcollinstn · 06-10-2003, 11:14 PM

Promax 300's are some big mothers.
If you're after 15" mids, you'd really be better off with twin 300 Drag motors. Much lighter, smaller cowlings, and 15" mids...

Philip · 06-10-2003, 11:21 PM

Toffen, just thinking about putting (2) 300's on a boat that is only 65" wide, (I did read that correctly?) makes you my hero. Why not try to put (3) 2.5's? they might fit!

Philip

GeeterB · 06-11-2003, 10:06 AM

tachyon · 06-11-2003, 10:31 AM

Where's the fuel for those bad boys go?

frequentflyer · 06-11-2003, 12:35 PM

Dude... That would rock.. I don't know if this is an option for you but Stainless Marine makes a nice Hydraulic jackplate for twin installation. This would give you the versatility to run higher or lower till you find the sweet spot. I should have bought it but it was not available when I got my plates. My motors are pretty close together but I would have to measure to tell you exactly but there is a minimum of 12" between cowlings.

dkwestern · 06-11-2003, 02:31 PM

I have never heard of mounting engines in a "V" configuration but i guess why not, it should work, and may even make the center of gravity better.

Toffen · 06-14-2003, 04:14 PM

Hi!

The Phantom 23 and 25 (as mine) runs twins (both 2, 2.5 and 3 liters engines) in the offshore cirquit in Europe. Then a second fueltank is added in front, making the balance of the boat better. I also have a ballasttank in front making it possible to rebalance the boat in high seas.

Current weight is:

Engine = 112 kilos
Powerlift = 35 kilos
Added setback 7,5 inches = 135 kilos

In total weight on the transom = 382 kilos

Two PM 300's direct on transom is 424 kilos. 42 kilo more than now.

MadEfi make 15 inches midsections.

Another and more expensive solution is to buy 2 x 2.5 EFI Offshores since they are lighter. What do you think?

Cheeeers, Toffen G