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Old 10-11-2013, 11:26   #1
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Repowering 1971 Whitcraft 45'

I posted this over in power section, and got no replies
Whitcraft 45' LRC

I understand this is very outside the box. I have been living on this boat going on 4 years now. Its an excellent liveaboard. And I could see this as a great LRC in inland, and coastal cruising conditions.

Anyone have any thoughts on this? What I want to do is pull out the twin v8s, and install two modern 4strokes off the transom. The idea is not to get the boat up on plane, just need trolling speed. Use for LRC, river/canal cruising etc. I'm thinking I want to be able to safely cruise at about 8 knots.

The transom is ridiculously thick and over built. Heck the whole boat is this way. I believe it would require no modifications to mount outboards by bracket. I could keep the twin 120 fuel gal tanks, port and starboard.

Emptying out the engine room would create a gigantic storage room, like for a motorcycle or scooter. There's a new Kholer generator already plumbed in. It would be a combination, generator/workshop, cargo bay.

How big do I need to go? How small can I really go?
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Old 10-11-2013, 13:28   #2
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twin 150 hondas or yamaha 4 strokes with a high thrust package will do that. Just a thought, outboards can pop out of the water in rough seastate giving little control. The amount of space you can gain is very nice however. My Experience with hondas is they are soo quiet! Not exactly sure but I think an inboard diesel would be much more efficient. Also outboards can have an effect on the apearance of the vessel.

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Old 10-11-2013, 16:05   #3
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Re: Repowering 1971 Whitcraft 45'

Thanks for your reply.

When you suggest twin 150's I assume you are talking about engines that would get the boat up on plane?

I'm talking talking about pushing the boat at 8-10 knots tops. By my calculations based on the planning-semi displacement hull, it needs about 40-50hp to move at 9 knots. Is that twin 30hp outboards

This photo is of a Whitcraft 50', basically same hull shape. Again all I want to do is push it at displacement speed for slow cruising.

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Old 10-11-2013, 17:07   #4
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Re: Repowering 1971 Whitcraft 45'

You're asking the question on the Cruisers Forum. From the perspective of a cruiser outboards would not be suitable for your boat. A pair of 120hp diesels may do the trick but advise from a Naval Architect would be advisable.

But yous are most likely thinking of using the boat as a houseboat. High thrust outboards are commonly used on house boats so finding a houseboat of similar size/weight/windage to your boat would give some good indications of what to get.

Manufacturers or dealers may be able to advise but again consulting a Naval Architect would be advisable.

There appears to be quite a few outboards for sale on on ebay but fitting a high thrust propeller may be necessary.
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Old 10-11-2013, 17:10   #5
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Quote:
Originally Posted by Mustang22 View Post
Thanks for your reply.

When you suggest twin 150's I assume you are talking about engines that would get the boat up on plane?

I'm talking talking about pushing the boat at 8-10 knots tops. By my calculations based on the planning-semi displacement hull, it needs about 40-50hp to move at 9 knots. Is that twin 30hp outboards

This photo is of a Whitcraft 50', basically same hull shape. Again all I want to do is push it at displacement speed for slow cruising.
Ah ok!

There is a 40 ft ply houseboat next to me which is powered by two 40 hp outboards and it does 10 knots at full throttle . How many hp were those twin v8s putting out? And what is the displacement of the vessel?
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Old 10-11-2013, 18:04   #6
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Re: Repowering 1971 Whitcraft 45'

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Originally Posted by Boracay View Post
You're asking the question on the Cruisers Forum. From the perspective of a cruiser outboards would not be suitable for your boat. A pair of 120hp diesels may do the trick but advise from a Naval Architect would be advisable.

....
??I'm aware this is the Cruisers Forum. Maybe I didn't explain.

What I want to do is take a 1971 Whitcraft 45' and turn into a "Whitcraft LRC." I want to get rid of the huge gas engines that suck fuel, and replace them with smaller modern outboards that are cheaper, lighter, more fuel efficient, and easier to repair. A small modern 4 stroke Honda 40hp would burn approx. 1 gal per hour. $6000/engine. Double that for two. I think this boat needs two, because it has twin rudders. There's ample space to mount them at the corners on transom. The transom is massive. A new engine is like 200lb/each. They would be fixed in place. Run throttle cables and wires. Fuel line into installed tanks.

With twin 120 gallon tanks that's a nice cruising range, plus u get to run the genset whenever u want AC on the hook. The empty engine room gives great storage. Imagine solar panels on the sundeck...

The boat has a layout that would work for extended cruising and liveaboard. Space, storage, tankage, etc. Its downside is the weight, sure, and the lack of displacement hull. It draws 3' feet, is 12" high and 12' wide. You could canal boat all day long, ICW, lakes, ANY costal cruising.

There are plenty of cruisers using modern low hp gasoline outboards to push their sailboats or displacement/semi displacement hulls at 8 knots. Think Rosbourough 24, or C-Dory, or Ranger, granted these are 1 screw...How about catamarans? or twin hull boats...Why would twin 30-40hp outboards not be suitable?

I'm looking at this repowering calculator
Boat Speed Calculator

The boat weighs 20,000lb with the current engines. Loose the engines and that's 1500lb right off the top.

I only want to cruise at a snail pace. And for the record, the Whitcraft 45' is a "Coastal Cruiser" not a houseboat LOL
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Old 10-11-2013, 18:08   #7
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Re: Repowering 1971 Whitcraft 45'

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Ah ok!

There is a 40 ft ply houseboat next to me which is powered by two 40 hp outboards and it does 10 knots at full throttle . How many hp were those twin v8s putting out? And what is the displacement of the vessel?
Original engines 2 x 225hp.
There was a diesel option back then for 2x 160hp
v-drives
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Old 10-11-2013, 18:29   #8
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Just remember, you don't want to run anything at full power for extended periods, for engine longevity and fuel economy, I'd suggest 50% power max for continous
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Old 10-11-2013, 18:55   #9
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Re: Repowering 1971 Whitcraft 45'

Also one should consider the amount of ballast provided by those V-8 lumps...is the righting moment going to change dangerously by removing them?
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Old 10-11-2013, 19:59   #10
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Re: Repowering 1971 Whitcraft 45'

I think what you want to ask yourself is, How Much Am I Willing To Devalue My Boat By Putting Outboards???? Rebuilt V8s are available for almost any brand for less than the cost of new 40 HP outboards, and wont devalue your boat. The basic engine of almost all gas V8s are auto/truck versions of well known makers. Transfer the marine parts and you have a marine engine. Also the worry about props coming out of the water is nothing compared to hitting a large wake, and having the bow raise, and the stern go down enough to dunk the outboards. Pay your dime and take your chances. _____Grant.
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Old 10-11-2013, 23:32   #11
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Petrol inboards make me very nervous IMHO
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Old 11-11-2013, 07:51   #12
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Re: Repowering 1971 Whitcraft 45'

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Originally Posted by a64pilot View Post
Just remember, you don't want to run anything at full power for extended periods, for engine longevity and fuel economy, I'd suggest 50% power max for continous
If you are dead set on going to outboards do as a64pilot recommends. 80 Hp per engine minimum so that you have the engines running at a relative low RPM when cruising: plus when you need it you have the extra thrust also when you need it. I would also believe you would be better off being able to steer the outboards than using the original rudders as they will be ahead of the props without the prop wash over them. Hey, just my 2 cents. Good luck with your changes.
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