Powerboat Forums at SpeedWake banner
1 - 20 of 31 Posts

·
Premium Member
Joined
·
6,826 Posts
Curious to see what the performance difference is.
 

·
Registered
Joined
·
36 Posts
Discussion Starter · #3 ·
That will be hard to tell as I have about 6 hours on the engine (383 350+hp) and I found when I got into the power band at 4000 rpm and 50mph it pulled hard to the right. I believe it was because of prop torque. I already had the DP, getting it ready, so I swapped it out hoping that with a prop turning each direction the prop torque will disappear.
 

·
I've Survived Everything!
Joined
·
12,273 Posts
If it works as well on your boat as it does on mine you'll be amazed at the hole shot!
 

·
Registered
Joined
·
36 Posts
Discussion Starter · #6 ·
Took it out for 3 hours this morning. Holy hole shot Batman! Like instantaneous. I had to put the trim bolt in the rear hole, as in the middle hole the bow was being pushed into the water. That worked great. Now just a very little use of the trim tabs are needed. Acceleration is excellent. Reverse is predictable and straight. I cannot believe how much better the boat handles. Almost no loss of speed when turning, although that may have a little to do with the torque of the 383.
The best thing is I no longer get prop torque at 4000+ rpm. That was unsettling. It now tracks straight and true, no matter how much power is applied.
The only downside is that it is a couple of mph slower 48 at 4000 before, now 45.5 at 4000. I'll take it.
Have not done WOT yet. Need a few more hours on the engine. I am sure as everything gets settled in and the rings seat, performance will only improve.
Cost for those interested:
Duoprop lower on ebay $1110.00
New seal kit, bearing and set up. $550.00
Stainless Steel C6 prop set. $980.00
total----------------------------$2640.00
 

·
I've Survived Everything!
Joined
·
12,273 Posts
mtnrat said:
Holy hole shot Batman! Like instantaneous.
Told you so! :bigsmile:

I couldn't believe how my 12,000 pound 33SS popped onto plane when we first tested one.

Not only will you realize a great hole shot, you will run your boat on less fuel with your duo-prop.

The downside is you do give up a tad on the top end. Something that doesn't bother me with my boat since I rarely run it at WOT.
 

·
Registered
Joined
·
3,516 Posts
mtnrat said:
The best thing is I no longer get prop torque at 4000+ rpm. That was unsettling. It now tracks straight and true, no matter how much power is applied.
I guess I was correct in thinking your leveling problem was caused from the torque of the prop then.. :winker:

I'm glad it all worked out for you.. :bigsmile:
 

·
Registered
Joined
·
36 Posts
Discussion Starter · #9 ·
Fyhr Factor said:
I guess I was correct in thinking your leveling problem was caused from the torque of the prop then.. :winker:

I'm glad it all worked out for you.. :bigsmile:
Yep you had it nailed. Took it to 55mph and 4700 rpm. Perfectly straight. I am just glad I already had the duoprop conversion in the works.
 

·
Registered
Joined
·
1,212 Posts
I think the only drawback to the dual-prop drives is top speed,
Mercruiser lists top speed reccomended for dual-prop drives is 65mph for thiers, dont know about the Volvo drive.
Curious to see what your top end will be. Sounds like a strong engine for that baot. Should be fun.
 

·
Registered
Joined
·
36 Posts
Discussion Starter · #12 ·
Wouldn't that be very difficult. I think I would have to raise the whole engine and fill and put a new hole in the transom??
 

·
Registered
Joined
·
3,516 Posts
Yes, difficult, costly & time consuming....
I can't see where your cavitation plate is in relation to the bottom of your deep V hull, but I think your good right where it's at...If you raised it much, you would just cavitate the prop's at wot..
Leave it where it is, and enjoy the boat.... :bigsmile:
 

·
Registered
Joined
·
1,630 Posts
The cav plate is for getting on plane - at speed it is not needed at all.

My cav plate is no where near the water line when at WOT and I have no cavitation.
 

·
Registered
Joined
·
36 Posts
Discussion Starter · #16 ·
Crap, raise the drive... Raise the engine mounts, raise the chick lounge, fill and cut a new hole in the transome, not adjustable, na 65 or so is fast enough for an 18 footer. :bigsmile:
 

·
Registered
Joined
·
8,878 Posts
Such a thing as a shortie lower unit for that drive?
Can they be "cut down" as an Alpha I once saw a thread on :)
Maybe then you can get near the "century mark" for top speed...
Raising it would be LOTS of work, but the more in the water, the more drag. So raising it WOULD get you some top end. MAYBE less low and mid (????) but, it's a decision wether payoff is worth the cost and effort too.
ENJOY the boat!!
 

·
Registered
Joined
·
3,516 Posts
Tinkerer said:
The cav plate is for getting on plane - at speed it is not needed at all.

My cav plate is no where near the water line when at WOT and I have no cavitation.
I think if my cav plate was no where near the water line at wot, my prop would be out of the water too..NO???? I have less than a 1/4" clearance between my prop to the cav plate and there's no water above the V hull at wot, so what's your prop pushing if it's in this area.. :confused1
 

·
Registered
Joined
·
794 Posts
mtnrat said:
Crap, raise the drive... Raise the engine mounts, raise the chick lounge, fill and cut a new hole in the transome, not adjustable, na 65 or so is fast enough for an 18 footer. :bigsmile:
Thats what I did minus raising the lounge.
 

·
Registered
Joined
·
19,039 Posts
Fyhr - I believe there is a lot more room in a TRS and Bravo than an Alpha between the cav plate and the prop. Try fitting a 32-36" pitch big diameter prop on the Alpha. Ain't gonna happen.

I actually plan on mounting my helmet cam to my transom so I can see if my plate is dragging thru the water. Also to kill two birds with one stone is to see how well the drive shower is working. I'm doing this because my propshaft centerline is about 7.5" lower than the hull.
 
1 - 20 of 31 Posts
Top