I/O (Sterndrive) Conversion to Outboards

[tphoyt]

Sweet

 

[jlh3rd]

I made sausage biscuits and cracked open another bottle of gin. In the south, we just wait a day ot two. Much easier. Couple three naps a day.

in our borough, we are supposed to clear sidewalks 12 hrs after the "event". It use to be 24 hrs. This is BS of course. Typical "white tower" overreach.
Who/What determines the "end of event" ? And what does "clear" mean?

 

[tpenfield]

Quick Update . . .

I had a follow-up call with the Naval Architect yesterday. He is going to run a speed/power analysis on the new hull configuration, given that there will be 42" of additional planing surface.

We've had some discussion on the transom, as he indicated the need for a solid core in the areas of the engine mounts (G10 material, which is epoxy-based). I had some concerns about epoxy vs. VE as well as the need for a solid core vs. the Coosa as the core.

After discussion, the light bulb went on . . . . . . The combination of the clamping force of the engine bracket and usage over time will tend to depress the core, if it were a 'softer' material, and weaken the overall lamination. It's a longevity thing. (OK, I get it ) . . . the Coosa is much 'softer' than the fiberglass.

G10 is wicked pricey, ($650-ish for what I would need) and not entirely friendly with the VE resin, but the N.A. suggested that I could make the core if need be.

So here is the plan . . .
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I'll cut out the 2 'engine mount' areas in the Coosa board and 'fill' the voids with fiberglass . . . probably will use some vacuum-assist to get a good density of glass. Then the entire transom will get more glass to build it up to a desired thickness. . . and even more glass for installation.

Works in theory . . .

 

[Scott Danforth]

Ask him about Aqua Steel

 

[tpenfield]

Ask him about Aqua Steel

I did . . . (not familiar with it). A lot of these materials (Aqua-Steel, Whalelite) are more direct to manufacturer type of sales/distribution. G-10, GPO-3 and a few others seem to have a wider use-base and can be found at more suppliers.

 

[redneck joe]

So, overall just a wee bit off...

 

[alldodge]

Going to be great
Maybe why builders like Formula just buy the brackets from Armstrong

 

[Scott Danforth]

I did . . . (not familiar with it). .

I will ask the NA at work on Monday. He is the one that suggested Aquasteel with VE

 

[tpenfield]

I will ask the NA at work on Monday. He is the one that suggested Aquasteel with VE

No worries. I am good with making the fiberglass core as I described. I got enough extra glass and resin to make a decent core . . . and it will bond itself to the Coosa.

 

[tpenfield]

Going to be great
Maybe why builders like Formula just buy the brackets from Armstrong

I like how Formula does their OB versions . . . they extend the hull/planing surface out to where the swim deck ends, then go with a bracket from there.

I'm not a fan of their swim deck with OB's . . . at least on the 310-330 series. I think on the bigger boats the swim platform area is more thought out.

 

[tpenfield]

On to the Transom . . .

I cut out the two areas for the fiberglass insert. My plan is to glass one side of the cavities and then 'fill' the cavities with a glass/resin combination to be level with the open side.

Here is the glass layer of 1808 setting up on one of the cavities.
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There is a 1" thick Coosa board (and plastic barrier) clamped underneath to keep it all nice and flat.

 

[tpenfield]

In other news . . .

I got the Hydrostatic & Speed/Power (Savitsky) analysis back from the N.A.

Not 100% sure what I'm looking at, but overall it looks good. I'll be having a follow-up call with the N.A. over the next few days.

In summary . . .

• No adverse trim effects from the added stern buoyancy & planing surface.
• Estimated speed is 52+ MPH with twin 300 hp engines. (the current boat does/did 45 mph).
• Loads are as predicted and in accordance with the design.

 

[tpenfield]

One thing that the N.A. was interested in reviewing, given the added buoyancy at the stern, was the trim angle of the hull. If the trim becomes 'negative', then the boat would tend to 'plow' at first when coming up on plane. . . not the best thing to have and would require compensating with engine trim, etc.

The analysis showed that while the stern may raise up a 'wee bit' from its original attitude, it still maintains a slightly positive trim angle. (a good thing)

Coming up on plane, the 'hump' angle is predicted to be about 7.2˚ . I'm not sure what the hump angle has been with the sterndrives, but it was a lot.

Here is a set of trim angle diagrams I put together, based on the analysis . . .
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I was interested in having the hydro-static and speed/power analyses done to see if there were any detrimental concerns of the design. Overall, things look OK.

 

[Pmt133]

Okay. I have a question. On the hump angle... my experience has always been that for the most part it's pretty close to dead rise until you climb on top. Ie my 19, 33 my buddies 38 etc... all basically rise to the point of obscuring view until youre out of the hole. I really doubt it's an exact correlation to dead rise angle other than more dead rise you have would seemingly equal more bow rise until on plane... that much makes sense to me. Same as more weight in the back would make it worse too...

Anyway, what I'm asking is, is that 7.2 degrees after you've hit planing speed or in that transition point? My 19 comes up at 16-17mph and is on top at 18ish. At 18 the bow is high but has dropped back down significantly from that of the 16-17 range. Then obviously as speed increases I add trim as the hull is pretty neutral... slight trim is worth 3 mph at wide open and about 400 rpm as the whole wetted surface lifts up and out vs riding on the whole bottom of the vee.

 

[tpenfield]

. . . what I'm asking is, is that 7.2 degrees after you've hit planing speed or in that transition point? My 19 comes up at 16-17mph and is on top at 18ish. At 18 the bow is high but has dropped back down significantly from that of the 16-17 range. Then obviously as speed increases I add trim as the hull is pretty neutral... slight trim is worth 3 mph at wide open and about 400 rpm as the whole wetted surface lifts up and out vs riding on the whole bottom of the vee.

The hump speed/angle is the highest angle of incline the boat reaches while coming up on plane. In terms of degrees of incline, it is nowhere near the deadrise angle . . . less than half. Because if it were close to the deadrise angle (18-23˚) folks would be loosing their beer coolers out the back in significant numbers.

This picture probably explains it best. . .

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It is the maximum angle the boat rises to before it starts to flatten out. It does generally coincide with when the boat begins to plane (+/-).

My boat 'was' the worst in terms of bow rise . . . and although not actually measured . . . was probably in the 8-10˚ range with the I/O engines.

 

[tpenfield]

I also have some data from the analysis as to how big 'a hole' the boat 'digs' in the water while coming up on plane and what the hull rises to as the speed increases towards WOT (50+ mph)

 

[Pmt133]

Thank you sir for explaining it like 2 year old i am. (Charts make everything easy)

Probably just seems worse than it is on the 33 due to how long it takes to plane and the loss of forward visibility. Those wellcrafts are notorious for running very bow high.

 

[tpenfield]

In terms of 'digging a hole' . . . here is the draw vs. speed
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At the higher speeds (30+ knots) the boat is pretty well 'up out of the water'.

As I leave a harbor or anchoring area, I often wonder what is a 'safe' depth to bring the boat up on plane. I usually wait until I have about 10 feet of depth . . .

 

[Pmt133]

Seems to more or less follow the prop slip curve as well... which makes sense.

Most of my area averages 5 foot depth so I'd be waiting a long time. Luckily the bottom is soft most of the time. The dredged parts of the ICW are deeper.