I/O (Sterndrive) Conversion to Outboards

[Scott06]

If I boated on a lake my current boat would be perfect for us as well. For the ocean, it is less than perfect. Not that any boat is actually perfect.

absolutely different environments/ uses and on a 21 ft the only place to hang out is back bench/sun pad/swim platform

 

[tpenfield]

In other news . . . I am seeing about a 12% improvement in fuel mileage, based on the battery upgrade project that I did this year.

 

[Scott06]

In other news . . . I am seeing about a 12% improvement in fuel mileage, based on the battery upgrade project that I did this year.

How ? just curious not arguing

 

[cyclops222]

Edmund Fitzgerald and British ship Hood. Come to mind.

 

[tpenfield]

How ? just curious not arguing

This . . . https://forums.iboats.com/threads/lifepo-batteries.765395/

Also got rid of a defunct refrigerator in the wet bar and took out some heavy tables . . . all totaling about 400 lb weight savings.

 

[Scott06]

This . . . https://forums.iboats.com/threads/lifepo-batteries.765395/

Also got rid of a defunct refrigerator in the wet bar and took out some heavy tables . . . all totaling about 400 lb weight savings.

ok so weight savings thats impressive

 

[Scott Danforth]

Not that any boat is actually perfect.

That is why you have 3

 

[Scott Danforth]

In other news . . . I am seeing about a 12% improvement in fuel

Ted, 1.12 x (boats suck at fuel economy) is still (boats suck at fuel economy)...... But that is a good bonus

 

[tpenfield]

The engineering department at Cruisers Yacht is telling me that the hull and deck molds for the outboard version of the 338 are different, which I sort of knew about the deck. I think it has to do with the balance point of the boat, since the OB version has the swim deck notched about 8" forward. So, I'm thinking these differences are for a reason, and probably not worth my venturing into the unknown.

So, the sell/buy option is probably my best play.

 

[tpenfield]

. . . OR . . . I would need to make similar mods to the swim deck and hull, so the engines hang in the same place as the factory outboard versions (which is right at the edge of the original swim deck).

Still in the paper analysis stage . . . . . .

Sell/buy options might be . . .

• CY 338 OB (only a few on the market, very pricey)
• BW Vantage 320 (more of a day boat, marginal overnight capabilities)
• Saxdor 320 GTO (European style boat, fairly new to USA market)

I'll probably continue to think about it through the season and decide over the winter ('wintah' as we say in Boston)

 

[Scott06]

I'll probably continue to think about it through the season and decide over the winter ('wintah' as we say in Boston)

Yeah maybe talk it ovah wihge your boyz at Dunkies...

Seriously really the only (boat swap) option given the costs and technology involved.

I would love to try wakesurfing without buying a surf boat. We have a 21 ft BR that I repowered back in 2016, looked into converting to VP forward drive or Bravo4S, just too much money / risk for backyard engineering (DTS etc) .. so I have resorted to lotto tickets

 

[Scott Danforth]

Ted, you need this. already comes with LifePo batteries...... and some really cool features. https://revelyachts.com/boat/revel-44s/

 

[tpenfield]

Ted, you need this. already comes with LifePo batteries...... and some really cool features. https://revelyachts.com/boat/revel-44s/

Very cool . . . but 44 feet is a tad over my mooring constraints. Besides, the Admiral does not let me spend that kind of $$$$$$$

 

[flashback]

Mutiny might work. Us tars have rights!

 

[tpenfield]

I did a little bit of measuring and math from the line drawings I have of the boat. I can understand why Cruisers Yacht has the bracket in such a position that the swim deck needs to be notched. It looks like they were trying to make the center of weight (mass) to be the same as the I/O versions.

 

[Lou C]

On some of the conversions I have seen with pods, the engines are so far back I can’t imagine that the balance of the boat isn’t affected. An I/O actually has better balance with the engines being forward and low….

 

[flashback]

When i was a kid my dad had an inboard Chris craft about 25 ft. With a 283 inboard. It was an easy boat to maintain. Handled real good accept at slow speeds. The rudder was kind of dinky.

 

[tpenfield]

On some of the conversions I have seen with pods, the engines are so far back I can’t imagine that the balance of the boat isn’t affected. An I/O actually has better balance with the engines being forward and low….

Hey @Lou C . . . I have noticed that the Formula boat outboard conversions are more of a bolt-on with little/no modification of the swim deck.

The Cruisers Yacht 338 OB has the swim deck notched out about 1 foot, so the engines mount right at the edge of where the swim deck would be. I think this has to do with maintaining the balance point.

The Cruisers 338 has the transom inset under the swim deck more than the Formulas, so it kind of makes sense that the Cruisers cannot be merely a bolt-on.

In terms of weight . . . just some rough numbers. . . The 6.2L sterndrive engine/outdrive combo weighs in at about 1,100 lbs each (big blocks are a bit more). The 300 HP outboard is about 600 lbs and the 350 hp is about 700 lbs. So, there does seem to be less weight with OB's, it is just further away from the 'balance' point. Obviously, the bracket adds some weight.

 

[Scott Danforth]

102" wide twin or triple engine outboard bracket like this is about 450# for the weldment. add about #50 for paint and fairing, and about #for each swim ladder

the fiberglass top cap and the teak, etc add weight from there.

 

[Lou C]

Some years back I considered buying a Shamrock direct drive inboard, these have the Keel Drive system where the prop is protected by a beefy keel, didn't buy because engine access was actually quite bad (probably could have been improved with some reworking of the opening in the deck) and the ones I could find needed a lot of work. BUT, simple SBF engines, Velvet drive transmission, very simple machines. Also, I'd have to learn a whole new skill set of single engine inboard maneuvering; though because I keep the boat on the mooring, it wouldn't be as bad as if I kept it at dock in the marina. Still if the right one came along, I'd consider it, because you get away from outdrives, and all their headaches, and keep the simple inboard engine, that can be closed cooled, probably the simplest marine propulsion other than a sailboat!