I/O (Sterndrive) Conversion to Outboards

[airshot]

Very personal decision based on health, age, retired or not, etc. One thing we can't change is time and it is indeed marching on. Tasks that I was exited about learning/doing 20 years ago now seem daunting. I'm finding the older I get the more the moon/stars have to line up before the boat goes out. Is downsizing not an option? Drop to a single, many greats boats out there in that category. What you think you have to have now may not be so in 5 years.

Life changes in a flash, live life to the fullest as long as you can afford it ! When we retired, we bought a used motor home to try it out....was great for the first two years, started looking at newer units and downsizing our home. Within a few months my wife had two hip replacements then two back surguries....non her fault.. Shortly after can barely walk, motor home sat for 18 months then gave up and sold it. Downsized the boat as she can no longer handle any wave action with her back. So....life can change in an instant, enjoy while you can !! Just a small 16' fishing boat to keep fish in the freezer. Only travel for us are trips to the doctor....

 

[Scott06]

Owner reviews on the Suzuki 300/350 duo-prop outboards seem to be OK. One thing that jumped out when looking at the spec's is that the 350 has 12:1 compression while the 300 has 10.5:1. So, I guess they are getting power from the compression as the blocks are the same displacement (267 Cu in) IIRC. Got to burn higher octane fuel in the 350's.

Just wondering if I can be OK with the 300's and use 87 octane gas. Most of the alternative boats that I looked at and of similar weight had twin 300's.

These are direct injected i would assume. since the timing of injection inhibits detonation they can use really high compression ratios again. Always a lot of discussions on compression on the muscle forums I am on. One of the engine builders mentioned difference between 9.5 and 11:1 compression is only like 3% or 4 % more power. So basically he was saying no sense pushing it for a few more ponies. Of course this is old school carbed engines.

i wonder if direct injected OBs suffer carbon build up on th intake path and valves like automotive engines do? this might negate some of the Maintenace savings of switching. What does the rough math on this workout to? Would think it would be half of the boats cost if not more to swap?

 

[Pmt133]

These are direct injected i would assume. since the timing of injection inhibits detonation they can use really high compression ratios again. Always a lot of discussions on compression on the muscle forums I am on. One of the engine builders mentioned difference between 9.5 and 11:1 compression is only like 3% or 4 % more power. So basically he was saying no sense pushing it for a few more ponies. Of course this is old school carbed engines.

i wonder if direct injected OBs suffer carbon build up on th intake path and valves like automotive engines do? this might negate some of the Maintenace savings of switching. What does the rough math on this workout to? Would think it would be half of the boats cost if not more to swap?

If the intake and PCV system is set up correctly, there should be minimal build up in the intake/valves on a DI engine. When I pulled my intake to replace my plugs at 100k (yes you read that correctly, stupid design) there was nothing much to note in there. Looked the same or better as any port injected engine I've had apart with that kind of milage. I know it's not typically the case but my experience is good. The ole Italian tune up helps too.

 

[tpenfield]

I'll probably price-out 3 engine options. Mercury, Yamaha, Suzuki and see how it all compares.

In 300 HP options The Merc is a V8, the Yammy and Zuki are V6
In 350 HP options, The Merc is a V10, the Yammy and Zuki are V6

IIRC, The Yammy used to be a V8 in the 350 HP range, but now they have bumped their V6 to 350 HP.

Yammy are the lightest engines and Zuki's are the heaviest.

Not sure any of the motors are supercharged . . . (any more like the old Merc Verado (L6) . . . probably a warranty repair item ? )

 

[Scott Danforth]

My former boss's boat has twin Suzuki 250's. Other than ECM issues, they have been ok.

 

[Stinnett21]

Also, I noticed that Suzuki now has dual prop lower units available on both the 350 and 300 HP versions. Just wondering about that vs. the single prop that the Merc and Yammy would have. It seems like Suzuki is making a strong play in the re-power market.

Others know more than me at this level but it seems having duo props on a twin installation would make no sense.

 

[tpenfield]

It is beneficial on heavier boats. That is why you see many twin engine boats with the Bravo 3 and the Volvo DX series outdrives. Now it looks like the outboards are getting in the game, since many boats that came with I/O are now going outboards.

 

[tpenfield]

Another set of pictures, based on refinements. I've taken some of the center sections of the internal structure pieces out (cut-outs) in order to save some weight. Also found a 3D model of the Suzuki duo-prop outboard.
.

.

.

.
The bracket will have about 44" of running surface with a step-up from the hull surface. Then there is about 20+ inches of notch leading to the engines. I will probably calculate the buoyancy of the bracket to get an idea of the change to the static waterline. I think the bracket will displace a lot more that the weight of the engines . . . it might raise the water line at the stern by an inch or so.

 

[Scott Danforth]

I would still look at hydraulic jack plates. that way you can get into skinny water as well as raise them out of the water.

 

[Stinnett21]

I see these center consoles with 6 engines and I just don't see how fiberglass alone holds up that weight/torque. It would seem like steel braces or something would be required. Even in your case...geez all that weight cantilevered over that far? Will there be any way to inspect those areas? Not trying to be a downer just an inlander wanting insight ha.

 

[Scott Danforth]

I see these center consoles with 6 engines and I just don't see how fiberglass alone holds up that weight/torque. It would seem like steel braces or something would be required.

most of todays boats, especially the ones with 6 engines bolted to the transom are carbon fiber

 

[tpenfield]

I would still look at hydraulic jack plates. that way you can get into skinny water as well as raise them out of the water.

Thanks, Scott. Looks like the jack plates are about $1,500 per engine. Probably a good thing to have as engine height will be a bit of trial and error (or testing and adjusting as optimists would say ).

I suspect once I get the engine height where I want it, I will not adjust it thereafter. Do the hydraulic jack plates have the ability to 'lock in place' ? What are the maintenance issues with jack plates? Would a mechanically adjustable jack plate be sufficient?

 

[tpenfield]

I see these center consoles with 6 engines and I just don't see how fiberglass alone holds up that weight/torque. It would seem like steel braces or something would be required. Even in your case...geez all that weight cantilevered over that far? Will there be any way to inspect those areas? Not trying to be a downer just an inlander wanting insight ha.

There are examples of too many engines and I would imagine that transom reinforcement is a significant consideration in those cases. Fiberglass is certainly strong enough, but the actual design is more important.

I did read through a conversion of a 38' Fountain where the owner went with 3 engines, yet 2 engines probably would have been better. The boat seemed to be too stern heavy and it took a lot of tweaking to get things right.

This (my) project is more in the typical realm . . . twin engines.

 

[alldodge]

You can get manual jack plates which have a center bolt to adjust height

 

[Scott Danforth]

the benefit of hydraulic jack plates is that you can adjust from the helm. used a lot on flats boats, etc. allows the motor to be lowered to bite on holeshot, and raised plane, and then really raised up to go in/out of skinny water at idle speed. by lock in place, that is what the check valves do

the added benefit is you can raise the motors before you tilt them to get clearance to your deck

the manual adjust will work as well for setting motor height.

 

[tpenfield]

New topic . . . Stern access.

I've been thinking about boarding/off-boarding access when at a marina slip for overnights. Typically, the boats are positioned 'stern-in' to maximize the available slip space and you get off/on the boat via the swim deck. Adding about 4 feet of bracket and outboard will potentially put the swim deck too far away from the dock and the typical ladder.

I've been thinking how to address this as part of the outboard conversion. Perhaps a temporary 'ramp' of some sort that can be put in place as needed . . . or maybe an extension of the bracket, similar to which some outboard boats now have as part of the swim deck.

Top views below of my boat with proposed bracket & outboards shown in gray tones.

1) Stow-able ramp to make the transition to the dock ladder


.
OR
.
2) Bracket Extension (wings) to have some walking area closer to dock/ladder.

.
3) ???

Thoughts, ideas, alternatives?

 

[dingbat]

New topic . . . Stern access.

I've been thinking about boarding/off-boarding access when at a marina slip for overnights. Typically, the boats are positioned 'stern-in' to maximize the available slip space and you get off/on the boat via the swim deck. Adding about 4 feet of bracket and outboard will potentially put the swim deck too far away from the dock and the typical ladder.

I've been thinking how to address this as part of the outboard conversion. Perhaps a temporary 'ramp' of some sort that can be put in place as needed . . . or maybe an extension of the bracket, similar to which some outboard boats now have as part of the swim deck.

Top views below of my boat with proposed bracket & outboards shown in gray tones.

1) Stow-able ramp to make the transition to the dock ladder

View attachment 402652
.
OR
.
2) Bracket Extension (wings) to have some walking area closer to dock/ladder.

.
3) ???

Thoughts, ideas, alternatives?

You’re going to leave your drives down while slipped?

Getting in and out over the transom is frowned upon due to safety concerns.

All the local marinas have finger piers every other slip. Allows you to access the boat over the gunnel

 

[Pmt133]

Just be that guy.... bow in.

 

[Lou C]

Our local marinas here in Long Island all have finger piers and the outboard boats all tilt their engines up when docked for any amount of time.

 

[tpenfield]

The overnight marinas in my area have a variety of slip arrangements, but you don't always have the luxury of getting what may be best. Many slip spaces don't have the finger piers; they just have pilings for the bow/mid-ship lines. So, the lines are at mid-ship and the stern.

Here is a recent example . . . Stern-in and in between the pilings at the bow.

.
Some boats stern in, some boats along side the dock. . . depends on what you get. Some I/O or inboards, some outboards. Note the twin Mercury 600's in the picture

.
Lots of variables . . . the slip space you get, the tides, wave action, etc. Tilt or not depends on water depth . . . A night or 2 won't kill the LU. I've only tilted up my outdrives when slipped if the depth was fairly low. Bow, in is not a great option either.

Anyway, not to argue a bunch of points, just want to consider the conversion design in light of the less desirable slip circumstances (i.e. stern-in).

Thanks for any ideas on the design.