Offset drive in narrow beam boat
 

Was told that if I offset the drive placement in my 7' beam boat it would help the boat stay more level under power. It kind of makes sense, but I would like some feedback. Boat is a 27 Excalibur, BBC and XR Bravo. The object is to try and keep the boat level without dragging a trimtab all the time.

Cheers,

Andy

Re: Offset drive in narrow beam boat
 

Joe Shaldenbrad of Sunsation Boats offset the engine in his 24 ft. Rockets and Aggressors about 3/4 inch to help compensate for propeller torque.

Re: Offset drive in narrow beam boat
 

I don't think there is an offset on my boat. I never measured or heard anybody mention it. The only time my boat leans to the left is at FULL DOWN trim. When I come on plane it leans but as soon as I give it a little trim it levels right out.

Re: Offset drive in narrow beam boat
 

Since it is a bravo, try running a left hand prop instead. It counters the torque. I have done it before, and have seen Fountains the same way.

Re: Offset drive in narrow beam boat
 

As long as your engine is Std. rotation BBC a right hand prop turns the opposite of the motor, not a left hand.

Re: Offset drive in narrow beam boat
 

lefty props do in fact oppose the engine rotational torqueon single engine application's. i have tested this on many small vee's with slight to very good results depending on h.p/ torque. you may also want to play with # of blades and diameter.

Re: Offset drive in narrow beam boat
 

Wouldn't running a left handed prop just make the boat torque roll in the opposite direction? :confused:

Re: Offset drive in narrow beam boat
 

No Boat; YES

Re: Offset drive in narrow beam boat
 

Center the drive and remount batteries or other things to make the boat run more level.

Re: Offset drive in narrow beam boat
 

Thanks for the comments. I'm leaning to the 3/4 offset. Will have to look into that a little more before I cut the hole.

Thanks,

Andy

Re: Offset drive in narrow beam boat
 

absolutely, rigging is your best friend when it comes to finding the correct c.g for a boat. as far as a lefty just moving torque from right to left , no. imagine holding a righty prop and running the boat. the boat would try to rotate to the left.so with a lefty the opposite would happen therefore eliminating a torquing problem normally associated with right hand application's.
also drive height plays an important role as does speed.
so does bottom straightness. hooks , rockers , etc,,,, .
this is what is known as dialing in a boat. the more home work you do the better your work will come out.

Re: Offset drive in narrow beam boat
 

So, if I read this right.

I check the bottom for anything other than straight.
Establish an X dimension. I assume that higher is better as I can always ad spacers.
Then determine the boats center of gravity with the components moved to make the boat balanced?
We were thinking of a ballast tank in the nose just in case.
Here's the next question, can you make the boat too stiff? I wanted them to stiffen the midships bulkhead and make the forward V Berth bulkhead go all the way to the deck. Also we are making an enclosed engine room bulkhead. So the boat will have three complete bulkheads instead of two.
Thanks for your help. I think I might be boating one day :rolleyes: You don't have a month to spare do you??

Cheers,
Andy

Re: Offset drive in narrow beam boat
 

And.............put the drive in middle of the boat where it belongs.

Re: Offset drive in narrow beam boat
 

absolutely. offset will induce some less than desireable results , some of which you will not find until speed. as far as bulkheads i don't believe this will hurt. it will add structural rigidity, just don't over do it as to create a negative in-balance of strength.
as far as the x goes higher is not always better. you should contact the manufacturer to see where they have set the heights for best top speed. then maybe add an inch, so you can always space down. keeping in mind the c.g of the engine. you can mount the engine lower and use a shorty to keep the balance.

example: x is at 17. mount it at 16(lower engine c.g) use a 2"shorty. you'll have an 18x.

also, an experience I had with a single engine 30 super boat. 18x dimension. used shorty. bad torque over and rode on the bow as well because the drive had no leverage. spaced it down 1 1/2 straightened out and picked up the bow. increased leverage .no more side lean,also picked up 2 mph because of less wetted surface.

in short good c.g to start with is best, as is a straight bottom.

good luck

p.s as afr as a month to spare , $ is king :rolleyes:

Re: Offset drive in narrow beam boat
 

[QUOTE=monstaaa as far as a lefty just moving torque from right to left , no. imagine holding a righty prop and running the boat. the boat would try to rotate to the left.so with a lefty the opposite would happen therefore eliminating a torquing problem normally associated with right hand application's.[/QUOTE]

I'm imagining it and I see a boat with a righty prop torquing to port and a boat with a lefty prop torquing starboard? :confused:

Re: Offset drive in narrow beam boat
 

i'm not imagining. i've tested this theory many times myself. with a few different manufacturers. kryptonite, superboat, donzi, activator, hustler, to name a few. water posseses a different law of physics.

so apply, if the boat has a hook or off x-dim. throw in different speeds and results become obvious.

Re: Offset drive in narrow beam boat
 

Now, for my next question.
Where is the correct CG. I would like to think that it would be right about where the driver would stand/sit. Is this the correct location with the boat loaded and everything positioned where it sould be?

Thanks for all you help.

Andy

Re: Offset drive in narrow beam boat
 

Play with the X center the drive do all hull balancing with internal weight changes, or you may induce something you can't fix without a lot of work. Personaly I would keep the X stock and go with a shorty, those results are more then well proven and not a myth in someones mind!

Phil

Re: Offset drive in narrow beam boat
 

:D

Re: Offset drive in narrow beam boat
 

Monstaaa I was imagining it because that's what you said to do(see post 6) :D

Re: Offset drive in narrow beam boat
 

gotcha.

lokk at the prop while the engine is running in gear, on land. it turn's to the right. if you were able to grab it, as to stop it from spining, and the engine didnt stall but it kept running, the boat would now spin to the left.
so if in the water and your torqueing to port, try a lefty wheel because it will torque to starboard.