Twin I/O to Twin Outboard Conversion Project

Another update to my 3D model . . .

The swim deck has a fairly large cavity between the top and bottom surfaces . . . probably about 7" of space. It will give me access to install the transom support struts and the fasteners on the top side of the "extendo-bracket"

Here are a couple of illustrations. . .
.
Swim deck . . .

.
Cavity between top & bottom of swim deck surfaces. . .

.

 

I think it looks awesome. Probably worth having someone well versed in coosa give some guidance on exact layup and layering. Outfit we bought from had a guy who took our numbers and helped convert it to a laminating schedule with our requested saftey factor. Might be worth asking supplier if they have some internal capacity like that or a recommendation.

Are you going to male mold and fair or make a one off female mold?

Like the duo prop 3d outboard in the mock up. Got to get a few hrs on repowered boat similar in size to yours that had the duo 300 suzukis. For the couple grand upcharge they seem to work very well at the lower speed node.

 

Thanks for your good words.

I have been contemplating how best to approach the mold process. I'd like to try to get an exact fit to the contact areas of the transom. One idea I have is to use the contact areas of the transom (orange color in the illustrations) as a female mold for just the 'outer shell' of those areas . . . probably a fair amount of CSM and maybe a layer of 1708 to make up a 'shell'. Then build the extendo-bracket as a male mold and attach the outer shell as a final step in the glassing process.

In other news, I got my first set of quotes on engines . . . a bit higher than I was expecting, but it seems to include all of the bells and whistles, which I don't need. I'll be getting a couple more price quotes over the next few weeks.

 

I will be getting the Coosa material from a specialty plywood supplier, so I'm not sure if they have any referrals on the glassing aspect. I anticipated that the engine installation shop might want some sort of documentation on the bracket, so I may run the plans by a local N.A.

 

One thing that I'm not sure about is the desirability of the 2" step from the transom to the extendo-bracket. I know many hull extensions are done without a step, and I'm not sure of the benefit of have a step vs. being even with the existing transom/keel.

Thoughts? experiences?

 

Ive found some wild shop to shop disparity on pricing. Not entirely sure how it ends up like that given the near commodity like nature of outboards. Searched some quotes from last October on identical 300 suzuki duo props, since nothings local it was 1800$ to get the boat 500 miles and 4500$ to get it to the lower 48. There was an 11,000 dollar spread for identical component quote requests. Kinda not surprised by that for the alaksa dealer but dealers we called down south separated by less than 30 miles had 4 to 5 grand differences in price per engine as well as a thousand per engine rigging cost disparity. Almost all the places had near identical amounts of reviews and ratings, but non trivial amounts of savings to be had by shopping around.

Seems like a good plan to pull the flange shape off the existing hull given its shape complexity.

Ive got no solid data points on the step at the transom. This spring we scanned a friend's hull that does very poorly around the 25knot mark. Its sweet spot is in the lower to mid 30s, unfortunately for our predominat sea state the holy grail is often though of between 22 and 26 knots. His step was probably more like 4 or 5 inches, they are welding it flush like a full hull extension and dropping the outboards down a few mount holes. The hope being that it may drop the top end but possibly give it better trim and planing surface at lower speed.

I've got no solid dog in the race as to if it will work, a very skilled young man is doing the welding off cut files we put together. If its a total flop.... well one of my only genuine skills in this life is my speed with an angle grinder and saw... cost of the project if its a flop is a rounding error on his retirement fun money so no big loss if it flops.

 

The more I read about hull steps, it seems that for a one-off instance, it would be pretty much guess-work. Additionally, steps in a hull seem to come into play at higher hull speeds, beyond what this boat will typically see.
.
Here is a rendering of the hull extendo-bracket without a step. There is a strake right at the chine of the extension, (not detailed in prior illustrations), which could be extended as well.

.

 

I realized after some review that the 2nd lifting strake on the hull will not line up with the outside edge of the Extendo-bracket. So I did a slight design change to have a transition of strakes going from the hull portion to the extension. Here are a few illustrations of the updated model showing the strakes.
.

.

.
So, I'll have a small gap at the transition . . .should be OK.

 

It's better .But I'll gladly repeat for the third time that it's even better to simply lengthen the hull with laminate. And forget about the trim tabs.

 

Some focus on the engine choices over the past few days . . .

I got some clarity on the Mercury vs. Mercruiser joystick systems . . . it has been a cloudy topic (for me) until recently. They are different products and it seems that never the two shall meet. It seems unusual, but I'm sure there is a story behind it. (feel free to chime in . . . )

Posting a summary here for anyone doing a similar conversion.

Mercruiser: The product is 'Axius', it works with Twin Engine Bravo 3 installations.

Mercury: The product is 'Joystick Piloting for Outboards' (JPO) . . . it works with Verado outboards in 2-4 engine combinations (can also work with single engine + bow thruster).

So, a Mercury or Suzuki outboard choice will require the Optimus joystick system. Yamaha can use their Helm Master EX system.

 

Tpenfield,

Why not extend the aft hull below the waterline and eliminate the trim tabs?

 

Do you really need this stuff ?

 

Had the opportunity to use the Optimus system last week. It was pretty nifty. Owner showed its features pulling away from the crowded harbor, and I used it at a remote dock. We got back to the harbor and it was a zoo with traffic. Never to the time to flip on the joystick, just docked regular with twins and the wheel.... so definitely not necessary but it did seem to work really well. From talking with them, they had Optimus on yamahas as well as suzukis and said it was the most refined of the mouse traps so they ran it on their boats across platforms.

 

No, I just want it . . .

 

I appreciate the comments and ideas, but . . .

IMO, trying to extend the aft fully width-wise, which I think is what you are suggesting, would really open up a can of worms and take things where I might not want to go. If the swim deck did not extend over the transom by the 3 feet that it does and the transom not have such complexities, it might be a different story.

Transom area and approximate waterline . . . There would be some 'interesting' cuts.


I'm going to keep the trim tabs . . . even if it was a full width extension.

Having looked at this boat for 4 years, I think an extension pod is a better way to go. I'll also note that if you look at the Formula 330 CBR (which is a very similar boat to this one) and their outboard versions vs. their I/O versions, they do the OB version in a very similar way (extending only the center section).