I/O (Sterndrive) Conversion to Outboards

[tpenfield]

Greetings . . .

I have been considering transitioning from having twin Sterndrives (I/O) engines and go to twin outboards.

I could do this in one of 2 ways . . .

1) Sell my sterndrive boat (Cruisers Yacht 338 mid-cabin bowrider) and buy a same/similar boat that has twin outboards.

2) Convert my existing boat (above) from I/O to outboards.

The cost to do the 'Sell & Buy approach' would probably be about 6 figures, given that the outboard versions of my boat are newer and more expensive in general. Similar boats to mine with OB's would be about the same uplift in $. Generally I like my boat's design and layout, as it is better than similar boats. The only negative aspect is the I/O's in salt water.

I believe I could do the 'conversion approach' for about 1/2 the cost of the 'sell/buy approach', but wanted to toss it out here for comment, insanity check , etc.

As for the outboard conversion approach . . . conceptually I'd:

1. Sell or trade-in my 2 Mercruiser 6.2L EC DTS engines (350 hours) and B3 outdrives, and buy 2 Mercury Verado 350 HP outboards (either lightly used or new)
2. Have a twin engine engine bracket (flotation style) custom made to fit my boat.
3. I figure that I can do the transom/stringer/structural mods and install the bracket myself.
4. I'd have an engine re-power shop do the fitting of the engines and controls.

One thing that I'm not quite sure about is:

• Would my current Mercruiser DTS, VesselView, and Axius systems be compatible with the Mercury outboards? (If I had to buy new, it would make the conversion a bit more pricey)

Perhaps there are some other considerations as well.

As for the sell/buy approach . . . I'd probably have to:

1. Sell my boat in a lakes region (maybe Winnipesaukee NH ?), since selling I/O boats on coastal waters is becoming nearly impossible.
2. Find the same boat in an outboard configuration, due the purchasing diligence, pay the sales tax, etc.
3. Make the boat my own with various modifications, fixes and upgrades that I have done to my existing boat.

Anyway, I'm looking for insights, comments, experiences, etc. I have been doing some Google searching on these types of conversions . . . most have been more simple single engine and lower tech types of conversions.

 

[Lou C]

Hey Ted,
Head over to the Hull Truth; there are a few people who have done those conversions on both classic boats (Bertram, Formula) and newer boats as well. For a job like this figure on using a really good glass shop for that part of the conversion. I thought of this briefly years ago but it didn’t make sense with my old boat. There are some unknowns like weight balance & center of gravity. When I’m done with the Four Winns I’m going to look at an Edgewater 18’ center console, in a year and a half I’ll be 70 & am tiring of I/O maintenance. Simple boat good for local bays around Huntington & Northport Long Island. Brand new. Done with fixing other people’s problems and especially with outboards want new.

 

[Chris1956]

A 33 footer will have the engines under the deck, and out of the way. Why do you want to change over? I presume you have a hot water heater. That will be a PIA to convert to OB power.

Rebuilt I/O engine blocks are pretty cheap. Outdrives are also pretty cheap (under $2K).

You could convert to closed cooling, if the salt bothers you. Engine blocks do last 20 years or more with raw (salt) water cooling. The manifolds do rot out every 8-10 years though.

 

[Lou C]

The problems of I/Os in salt can’t be appreciated unless you’ve been maintaining one for some years. Moored boats you will get marine growth no matter what the anti fouling paints for alu just don’t work that well. Ted’s engines were closed cooled from the factory so that’s covered. No one here is buying sterndrives anymore. At the Nassau County Boat show (Long Island NY) I saw a few inboard boats and I/Os but the great majority are outboards. The coastal salt water market has totally shifted.
As for me as much as I love Chevy small blocks here in the salt pond for the future outboard only. I’ll take a Chevy in a hot rod in a boat the old school mechanics call I/Os double trouble lol. I’ve done really well with mine but it took hrs of regular maintenance EVERY year!

 

[alldodge]

I would suggest Formula 310 or 350 depend on how much allowance the Admiral says is ok. I would not convert, if for any other reason you may never be able to sell it afterwards

 

[Chris1956]

Lou, I understand the trends you see. I see them here as well.

Now if you want to make the conversion or sell/buy a new boat for 6 figures, that is a way to go. I am not sure it is worth it to defeat the barnacles and the sterndrive maintenance. Have you tried brushing on Trilux or some other aluminum boat A-F paint? The spray A-F was crap.

A boat like yours is designed for I/O power. It has the configuration and integration for them. Changing over to outboard power can be obviously done, but the transom would need to be beefed up, or a bracket added. I have not priced those 350HP OBs, but I would expect them to be $30K each.

You will have a nice large empty engine bay when you have converted. What are your plans for that space? Generator is a likely choice, as is A/C.

 

[tpenfield]

The current engines are the SeaCore versions, so they have full closed cooling.

Good point about the water heater, It would only be useful on shore power.

I'm with Lou on the attraction to OB's . . . I'm getting too old for this stuff with I/O's . . . engine access and annual maintenance are a PITA.

If I did the Sell/buy approach . . . I'd be going from a 2016 Cruisers Yacht 338 I/O to a 2019-2022 (ish) Cruisers Yacht 338 OB. Same HP. (700 total).

I think the main difference would be the cost, which would be about $50-70K more to 'upgrade' than to do a 'conversion'. But the extra cost may be worth it in terms of less hassle.

 

[tpenfield]

One of the nice things about this (my) boat is that it was offered in both I/O and OB versions. So, it can be seen as to how the bilge area and structure is modified/reinforced to accommodate the outboard bracket, etc.
.

.
I contacted a local re-powering shop to see what they have to say about a conversion. I'll also reach out to Cruisers Yacht to see if they have any guidance.

Just crunching some numbers, I'm leaning towards a conversion vs. a sell/buy because of the difference in cost, and about $18K of it is for sales tax on the 'new' boat, which is a throw-away.

 

[Scott Danforth]

The bracket alone will be over $10k

Not sure outboards are that much better. They suffer barnacles and other issues when moored just like I/Os

Personally, I would sell what you have and buy what you want

 

[Lou C]

While big outboards have become complex and can have problems the balance is that they can tilt out of the water unlike I/Os and you don’t need the complex the interaction of the transom mount swivel housing & pivot housing & tilt n trim. On I/Os the engines are simpler but the adaption to marine use is complex often with poor access for repairs. With outboards the engines are complex but without the additional complexities of the drive system. I also think in general outboards are safer. For small boats there’s no contest outboard all the way.

 

[flashback]

Something tells me your not happy. You have poured tons of labor and cash into this boat, what do you want.

 

[tpenfield]

Something tells me your not happy. You have poured tons of labor and cash into this boat, what do you want.

Fair question. I am getting tired of keeping up with I/O's in the salt water (I think @Lou C can relate). I can do it, but my preference would be to have outboards.

I have considered getting a different boat that has outboards, but none that I've found have a layout as good as what I have, and/or would cost a whole lot more than doing a conversion.

So, I like the boat, not in love with the engines.

 

[tpenfield]

The bracket alone will be over $10k

Not sure outboards are that much better. They suffer barnacles and other issues when moored just like I/Os

Personally, I would sell what you have and buy what you want

Scott,

I see that there are a few brands of brackets . . . Do you know of the better brands and perhaps the ones to avoid?

My ideal 'swap' would be sell my 2016 I/O 338 and buy a 2019 or newer OB model Cruisers Yacht 338 - same boat. But, the cost bump-up is pretty steep. I could do a bit of a wait 'n see on the price difference a few years out.

 

[Stinnett21]

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.

 

[Scott Danforth]

Scott,

I see that there are a few brands of brackets . . . Do you know of the better brands and perhaps the ones to avoid?

We build brackets for some OEMs at work. Armstrong has a good reputation. However the build quality on all of them are iffy since it's considered a commodity.

Most are low-overhead mom-n-pop fab shops building them in a weld bench. We have to cut margins to be competitive

I would recommend to find out who makes the bracket that Cruisers uses and get the same.

If you are thinking of a conversion. There are deals to be had now with the whole industry in a slow market

The pod to hull caulk seam is a maintenance point as it's a bolted seam under the water line

 

[flashback]

You've got everything else set up just how you like. Why not have the outboards. I get it.

 

[tpenfield]

We build brackets for some OEMs at work. Armstrong has a good reputation. However the build quality on all of them are iffy since it's considered a commodity.

Most are low-overhead mom-n-pop fab shops building them in a weld bench. We have to cut margins to be competitive

I would recommend to find out who makes the bracket that Cruisers uses and get the same.

If you are thinking of a conversion. There are deals to be had now with the whole industry in a slow market

The pod to hull caulk seam is a maintenance point as it's a bolted seam under the water line

I have an email into Cruisers to get their advice. I'll try to find out where they get their brackets.

I was wondering about the pod-to-transom seal, as many of the brackets have an open face. I think I've seen some that are closed face. I wonder why they are not all closed face?

 

[Lou C]

The only way I’d have another I/O would be a larger boat single engine with a wide open engine compartment easy access no pulling out seats or other nonsense to do an oil change & pull drain plugs. It would also have to be old enough to predate the mandate for Cat Converter exhaust because there’s no way I would want an expensive pair of heat generators in the engine room of a fiberglass boat!
That, I absolutely will not accept. If outboards don’t have them I don’t see why inboard owners are unfairly penalized by the cost of replacement for those systems. $4500-$6000 parts cost vs $1500-$2000 and even less for good aftermarket. Remember in the salt you are replacing these every 5-7 years depending on how salty the water is.
For me as a practical matter all I’ll ever really have is a 20’ boat (storage, towing etc) and for that size outboard for sure.
I’d be curious to hear what Cruisers says about a conversion..

 

[Scott Danforth]

I wonder why they are not all closed face?

because getting metal to match a molded transom curve is really really really expensive. things move and make installation easier without it being boxed in.

 

[KJM]

The only way I’d have another I/O would be a larger boat single engine with a wide open engine compartment easy access no pulling out seats or other nonsense to do an oil change & pull drain plugs. It would also have to be old enough to predate the mandate for Cat Converter exhaust because there’s no way I would want an expensive pair of heat generators in the engine room of a fiberglass boat!
That, I absolutely will not accept. If outboards don’t have them I don’t see why inboard owners are unfairly penalized by the cost of replacement for those systems. $4500-$6000 parts cost vs $1500-$2000 and even less for good aftermarket. Remember in the salt you are replacing these every 5-7 years depending on how salty the water is.
For me as a practical matter all I’ll ever really have is a 20’ boat (storage, towing etc) and for that size outboard for sure.
I’d be curious to hear what Cruisers says about a conversion..

Another thing I always worried about was if a bellow springs a big leak, you have a big hole in the back of your boat below the waterline!