Coverting an I/O into an outboard with an extension

Hi,

I am looking at coverting my 22' bayliner I/O into an outboard with a 22" bolt on extension. Any suggestions on the best way to mount it, pro's and con's etc. would be helpful.

Thanks

 

There are several threads on this subject. The main problem is that the weight you shift aft will make the boat porpoise. Also, the structure of a I/o hull is different from and outboard.

 

Considering that you would strengthen the transom to accomadete the weight of the transformation , and that the O/B is much lighter than the I/O, and that the space of the I/O now left empty that could be used for an added fuel tank or other..... would the boat still porpoise ?

 

May as well buy a new outboard in this case. I/Os seem to corrode and are less manuverable by virtue of their design.

 

The center of gravity will be shifted aft by a large amount. Maybe large trim tabs could counteract the change.

 

If it's some sort of outboard, can't you just trim the whole outboard unit?

 

Not really. As the center of gravity moves aft, lift must also move aft. Trim tabs provide dynamic lift.

 

If you knew the approximate position of the boat's centre of gravity, it would be possible to calculate the effect of removing the inboard and installing the outboard. At a guess it is probably around 55% of the waterline length aft of where the bow meets the waterline. Unfortunately in a boat like this, there isn't much in the way of permanent onboard weight that you can relocate forward to counteract the shift in the CG. You're one up in the sense that the o/b should be significantly lighter than the sterndrive... but then you'll have the weight of the bracket to contend with too.
Which basically leaves you with Gonzo's suggestion of installing big trim tabs, which as he says may or may not address the potential for porpoising.
I'd whack a new sterndrive in it - cheaper and less chance of turning the boat into a complete dog!

 

One of the biggest problems the boat has now is it is very bow heavy, scary in big trailing seas. The extension is a fiberglass mold made to follow the boat. It is 52"W X 30"H(at the keel) and 22"D. I have been told that this will give the aft portion bouyancy and act as a giant trim tab. I will use the existing engine well for storage so the weight will essentially be the same just a bit further back.

Thanks for all the advice!!

 

It looks almost like a hull extension. Have you talked to anyone that made the change in a boat like yours? There is nothing as a finished product to see if it works.

 

I have spoken with about 4 people. Most of them bolted it on, glassed over it and mounted their mototrs. The mold is coming from a boat manufacturer and he sells quite a lot of them here in Hawaii.