I/O (Sterndrive) Conversion to Outboards

[redneck joe]

Red is finer than other colors

Come to think on that, I did experience that once and I have to agree.

 

[Scott Danforth]

Ted, the one or two repairs to the Coosa show that you were "shy" at least once.....

 

[Lpgc]

Come to think on that, I did experience that once and I have to agree.

not too shy then

 

[redneck joe]

not too shy then

 

[flashback]

or maybe: How many little marks did you say?

 

[tpenfield]

Ribs, Gussets and Lateral Supports . . . so as to get back on topic.

It has been slow going, but I am getting my arms around the details of the internal structure of the extension pod. As I proceed, it is occurring to me that maybe I over-designed this a 'wee bit', but who knows.

Since Cape Cod has somehow moved to within the Arctic Circle, I have been tenting the extension pod and running heat inside it to get the VE to cure. I can keep the inside area about 82˚F while the garage air is about 58˚F


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I decided the sidewalls needed ribs to stiffen it them up . . .

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The main center girder has an section that may need to be more stiff to prevent/deter buckling under compressive loads. So, I added some stiffeners.
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On the secondary stringers, which are in line with where the engines will mount, I wanted to have a similar resistance to buckling. That will be accomplished by a lateral rib, cutting the unsupported distance in half, which gives 4X the buckling strength.
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I also put in the lateral supports . . .

And then there are the gussets . . .

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There are a few more gussets to be installed along the 'top' section. Everything is tacked into place now and I spent part of the day doing fillets in preparation for glassing everything solid.

My little space heater has done the trick so far. Mid-week, we are supposed to hit 50˚F during the day, which should help the progress.

 

[Scott Danforth]

Ted, there is never over-designed.

 

[redneck joe]

Ted, there is never over-designed.

Until y o u have to tear out your own work. Me and my brother laugh about that as we build. He's never been here to tear out the sh...t we built the sob.

 

[alldodge]

Ted, there is never over-designed.

I would disagree with a boat
The more weight you add the more fuel is used to push it

 

[tpenfield]

I would disagree with a boat
The more weight you add the more fuel is used to push it

My 'target' weight is 400 lbs. for the extension pod. I think I'll be about that.

 

[redneck joe]

What is net tho? Im sure you covered that already.

 

[Lpgc]

Look forward to seeing some pics / video of it on the water when its done.

I noticed some boats on the river near me had inboards removed and outboards fitted but only small outboards to use for cruising the river and inland waterways, nothing like the effort or engineering going into this.

Congrats on getting so much done already @tpenfield , do you expect it to be done by spring?

 

[tpenfield]

Quick Update . . . Structural finer points.

One of the concerns I had about the structural design was a fairly long run of the secondary 'stringers' (about 42") vs. their width (~ 0.75"). These stringers (perhaps more like girders) are in line with the engine mount locations, so they will have a fair amount of direct load on them. The top of these stringers are unsupported and the bottom will be bonded to the planing surface of the extension pod. (Stringers in a boat are normally attached to the hull at the bottom and the deck (or boxed in) at the top).

So, the stringers can be considered as long, narrow members in compression . . . acting like columns . . . and columns have a 'buckling' point at which they can no longer support the load. Based on some of my force and G-force calculations I did not want to leave these to chance. So, I added a cross member at about half way along the stringer. (purple arrow) The effect is to shorten the 'column', making it act like 2 columns stacked instead of one. Engineering-wise, shortening the height of a column by half provides 4X the buckling strength.

These cross-members will provide lateral support to the top of the stringers giving them the added strength.
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Starboard side . . .

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The lateral supports were nearly the same dimension, (about 18"), confirming my dimensional symmetry. The port was 'shy' and the starboard was 'strong' (by 1/32")
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port side . . .