Chris craft 280 converted to “trawler”

[Nomad Willy]

Bill I assumed anyone would put fender washers under the bolt heads and they should be bolts not screws. The 2x4 ideally would go just under the screw clamps of the engine mount. The transom is probably strong enough and I see the 2x4 as mostly stiffness. Before rubber engine mounts transoms acted like drum skins and radiated lots of low frequency noise.

I see you like big gassers so it’s natural you’d recommend keeping the old engine. And I like outboards .... go figure.

But I think I’d wand the outboards for the great maneuverability they afford and the trip the OP is contemplating would probably involve lots of close quarter maneuvering.
And running a planing hull at 6 knots performance would be better w the heavy inboard engine gone. If the boat is kept light it should only require about 15hp total and high thrust outboards should deliver.

 

[KnotYet]

I'll add what little I know to the rest:

The existing engine is most likely a small block Chevy and could be fixed or replaced
for the cost of one new (or a pair of used) 25HP outboard(s).
You would then have a boat you could enjoy with fewer compromises and no mods.

JMHO.

(edited after reading Nomad Willy's post below)

 

[Nomad Willy]

Everybody seems to think the guy needs new outboards WHY?

Why would a guy w a 35yr old boat need new engines?
If he had the money he’d prolly buy a 10-15yr old trawler.
Or an older trawler like mine.

 

[rslifkin]

The existing engine should definitely be a small block Chevy, probably with a Velvet Drive 71C behind it. Most were 305s from the factory I think. A rebuilt marine long block 305 or 350 should be in the $2000 - 2500 range. Add new exhaust manifolds and risers and the boat can probably be repowered in kind for $4000 or less depending on how much work needs to be paid for vs DIY.

If a slower, more efficient boat is the target, there are plenty of other engines that could be found / installed with the original driveline arrangement.

Outboards would save some weight, but I'm not sure what they'd do to weight distribution. And reconfiguring the fuel system, controls, steering, etc. to run outboards, get rid of the existing rudder, etc. would all be a good bit of work. Probably enough that the outboards just don't make sense in the long run.

 

[Solly]

Former CC 280 owner here. My 2 cents...
It could be done. Yes the transom will need reinforcement and bracing. No access to the outboards from the cockpit w/o contortions. Mounts, steering, throttles and shift are all DIY.
Only you can decide if you can or should do it.
But... You can run the small block at idle or 1000 rpm and do the same thing. You don't have to run wide open.
On mine the absolute best money I ever spent was on a bow thruster. Installed it myself. That takes care of maneuvering.

 

[Bill V]

New engines are not needed but ever try to find a used electric start, long shaft, remote steering, high thrust outboard used? Let alone a counter rotating prop for one engine. If both engines have the same rotation there goes “close quarter maneuvering“. Am I correct in assuming you want to hang the engines on the existing transom?

 

[Portage_Bay]

Don't outboards deliver most of their thrust to swing the stern by steering direction vs prop rotation? I've run lots of single outboards and noticed no prop walk. They were very maneuverable in close quarters.

New engines are not needed but ever try to find a used electric start, long shaft, remote steering, high thrust outboard used? Let alone a counter rotating prop for one engine. If both engines have the same rotation there goes “close quarter maneuvering“. Am I correct in assuming you want to hang the engines on the existing transom?

 

[Bill V]

Don't outboards deliver most of their thrust to swing the stern by steering direction vs prop rotation? I've run lots of single outboards and noticed no prop walk. They were very maneuverable in close quarters.

That is true with singles as you can easily correct for prop walk with the steering. Virtually all twin engine outboards have the props operate in opposite direction just like twin engine inboards. Granted in most cases we're talking about a minimum of 100 hp twin setups. In the case of 25 hp twin set ups it might not be as big an issue.

Bill I assumed anyone would put fender washers under the bolt heads and they should be bolts not screws. The 2x4 ideally would go just under the screw clamps of the engine mount. The transom is probably strong enough and I see the 2x4 as mostly stiffness. Before rubber engine mounts transoms acted like drum skins and radiated lots of low frequency noise.

I see you like big gassers so it’s natural you’d recommend keeping the old engine. And I like outboards .... go figure.

Yes, I like horsepower because I travel long distances at times to fish and don't want to spend all day getting someplace. MY previous boat was a 2440 Robalo with twin 225's and cruised at 30 knots to the fishing grounds. Present boat does the same all day long but admittedly at a higher fuel cost.

Converting an inboard to outboards is a big task and one that needs a thorough game plan. Read about how this guy did his and has done many before and afterwards. https://www.glasply.org/forum/technical-forum/restoration-repair/7818-1981-24-outboard-conversion

 

[Bill V]

Former CC 280 owner here. My 2 cents...
It could be done. Yes the transom will need reinforcement and bracing. No access to the outboards from the cockpit w/o contortions. Mounts, steering, throttles and shift are all DIY.
Only you can decide if you can or should do it.
But... You can run the small block at idle or 1000 rpm and do the same thing. You don't have to run wide open.
On mine the absolute best money I ever spent was on a bow thruster. Installed it myself. That takes care of maneuvering.

Spoken by a man that knows from experience. Yes, anything is possible but is it practicable.

 

[High Wire]

Replacing 1500 pounds of cast iron with 300 pounds of aluminum outboards will change the ride characteristics. To what, who knows? You don't want it to roll over when the ballast is gone.

A big outboard bracket like ones from Armstrong might work. Its probably going to be custom anyway. I would get one you can stand on to work on the OBs.

Counter rotation not needed going that slow. Nor trim tabs.
Even two 9.9hp 4 stroke Remote, 25" shaft meant for sailboats might make 6 knots.

 

[KnotYet]

Replacing 1500 pounds of cast iron with 300 pounds of aluminum outboards will change the ride characteristics. To what, who knows? You don't want it to roll over when the ballast is gone.

A big outboard bracket like ones from Armstrong might work. Its probably going to be custom anyway. I would get one you can stand on to work on the OBs.

Counter rotation not needed going that slow. Nor trim tabs.
Even two 9.9hp 4 stroke Remote, 25" shaft meant for sailboats might make 6 knots.

More like only 600 lbs for a small block and trans but your point is still valid.

 

[High Wire]

More like only 600 lbs for a small block and trans but your point is still valid.

Sorry, I was thinking twin SB's.

 

[rslifkin]

Small block and trans is definitely more than 600 lbs. Figure 150 lbs for a reduction gear Velvet Drive plus 750-ish lbs for the engine (with all of the heavy cast iron manifolds, risers, etc.). So probably in the 900 lb range total. A fully dressed marine big block with all iron parts is darn close to 1000 lbs and a small block should be 200 - 250 lbs lighter.

 

[Boat brain]

Wow wasn’t expecting all these responses, haha. I should clarify ,I don’t own any boat currently. This was more of a hypothetical. Thank you all for taking the time to answer. I see that there’s a lot of knowledge to be gained on this forum.
So someone mentioned that I should just get a boat that is built for the purpose that I would use it for. That would sure simplify things. Boats that appeal to me are something like a C-dory 26(out of my price range) or the nimble nomad(can’t find any for sale , and probably out of my price range). Other pocket trawlers are rosburogh24 , ranger 25 ... basically all the diesel pocket trawlers under 30 feet are out of reach for me. And buying an old marine trader 34 or main ship and having to repower would put me in the poor house. Also I want to keep it under 30ft. Let’s say my budget is 25k. So I though maybe it would be possible to make my own cruiser powered by small outboards. I want to go slow and burn little fuel. I don’t really want to repower a large gasser inboard. I may be mistaken but my understanding is that even at hull speed you are getting 1-1.5 mph with a big gasser. Again I could definitely be mistaken . I’m just going off research not practical experience. I was able to find one old thread where a guy repowerd a 25ft I/O cabin cruiser with a 50hp outboard and claims to have gotten 7-8mpg at 7mph . That seems awesome . On par with the nimble nomad. Even if the guy was a exaggerating and it was half that good. I would be happy .
So I figured I could find a sub 30ft cruiser with a junk engine cheaper because I’m just going to remove it and turn it into a boat that I want . I chose the CC280 because I like the lines better then the more modern express cruisers. A few of you mentioned that the transom of an I/O is stronger and may lend itself better to this kind of project. Maybe I should consider finding an I/O.I have seen a couple of guys on YouTube convert I/O bay liners to outboard .
It was something like glass in a plug for the out drive hole. Add a layer of plywood to inside of transom. Bolted on bracket , everything was sealed with 5200 .added steel bracing between the stringers and inside of transom , I guess where the motor mounts were. To transfer load and provide strength.
Obviously this is easier said than done. But it doesn’t seem impossible.
Any way thanks again for humoring me.
All the info and opinions are appreciated.

 

[rslifkin]

I'd expect a 280 with a single small block could manage 2 mpg or a little better at low speed. If budget allowed at some point, a diesel repower could save a bunch of fuel. Plus, a cheaper boat at the start buys a lot of extra fuel.

 

[Solly]

Just to give some more helpful advice ( I hope ). A 25' boat will have a beam of about 8' Meaning little interior room. 28' + about 10'. Big enough for 2 with more comfort. Once you get over 10' beam a boat can get down right roomy. A smaller/lighter boat will get better fuel economy but with a reduced living space. Beam makes all the difference in space. It takes a certain amount of fuel to push a mass thru the water. The above are all generalizations.
Fuel economy shouldn't be your first consideration with a boat. At best you will find one that's 'acceptable'.
Go out and get on boats. As many as you can. Make a list... Must haves, like to have, not important. Check each boat against your list. Find one that checks most of your list. And as you get more knowledge your list will get better and closer to what you need.
Have fun !!

 

[Bill V]

Just to give some more helpful advice ( I hope ). A 25' boat will have a beam of about 8' Meaning little interior room. 28' + about 10'. Big enough for 2 with more comfort. Once you get over 10' beam a boat can get down right roomy. A smaller/lighter boat will get better fuel economy but with a reduced living space. Beam makes all the difference in space. It takes a certain amount of fuel to push a mass thru the water. The above are all generalizations.
Fuel economy shouldn't be your first consideration with a boat. At best you will find one that's 'acceptable'.
Go out and get on boats. As many as you can. Make a list... Must haves, like to have, not important. Check each boat against your list. Find one that checks most of your list. And as you get more knowledge your list will get better and closer to what you need.
Have fun !!

That is some very good advice. My boat hull is 28' 9" long and has a 10' 11" beam. My wife and I have lived on it for up to 3 months and found it comfortable. It has a built in freezer, propane furnace, full galley with propane stove/oven and refrigerator as well as a 3.5KW generator. Total remodel of cabin interior and 2 additional fuel tanks added to increase fuel capacity to 200 gallons. Water is 85 gallons. I say all this to give you somewhat of an idea of what can be accomplished with a 28-30' boat IF you have some beam. I have a V berth and a very nice single berth with drop down table in dinette. It can be done but it takes money and skill with a place to do the work. I have spent 15 years building this boat and have added a transom door, dinghy davits (9' RIB) and larger/stronger swim platform. I have dual chartplotters, depth sensors and Radar. I have Simrad auto pilot for slow cruising at 6-8 knots for 2.4 - 2.6 mpg as shown on my FloScans or 1.1 - 1.2 mpg at 23-26 knots. Top speed is 38 knots. I am Alaska bound as soon as the Canadian border is open again.

 

[Art]

IMO - IF I were to alter an inboard boat [single or twin screw] to two [2] o/b's. And that's a huge, huge IF! LOL

I'd place the o/b's as wide to the sides of transom as possible and have separate throttle/thrust-direction controls for each. I'd have both tied into one steering unit so both drive units are always in similar position/direction.

Reasons:

1 - Could maneuver ok while going slow speed in close quarters... by leaving engines set straight ahead and shifting forward or reverse for each. And... being able to powerup on either engine when it's in forward or reverse. This would make boat control while docking much like having twin inboards. Although a bit different due to smaller props, no rudders and different configuration of prop-thrust gear box on o/b's.

2. By having engines wide on sides the center of transom could have a swim step for many fun-use reasons. Also, the center swim step would allow work on either o/b's inner most side and on its top.

3. By having o/b's on outside transom edge the engines outer most side could be worked on by being at a finger dock or in a dingy.

4. By mounting o/b's at outside edges of transom the mounting brackets could be affixed to the transom and wrap around for fastening on boat sides. This relives stress on mid transom.

Happy Boat-Alteration Daze! - Art

 

[Bill V]

I'd place the o/b's as wide to the sides of transom as possible and have separate throttle/thrust-direction controls for each. I'd have both tied into one steering unit so both drive units are always in similar position/direction.

Reasons:

1 - Could maneuver ok while going slow speed in close quarters... by leaving engines set straight ahead and shifting forward or reverse for each. And... being able to power up on either engine when it's in forward or reverse. This would make boat control while docking much like having twin inboards.

Phenominal idea and with practice could incorporate steering into the equation as well.

 

[Nomad Willy]

Very good advice Solly,
If Mr boat brain could find a good 28’ inboard for cheap perhaps he should try it out first. One can dink w a carb and through lean jetting lower the fuel burn.

But per the above posts about weight it would still be more draggy than if equipped w OB’s. And since the OP needs to watch his expenditures the OB may be easy to beach ... for painting ect.

But re the weight if the inboard is fairly far fwd the OB’s may be a benefit to trim issues and not a problem.
An other thought is removing the old engine could (if it was well fwd) make the boat when converted to OB’s better balanced and almost certainly more seaworthy. Original placement of the engine may have been decided partially re considerations re the boats beam. So the more beamy boats may have the engines further aft or they’d be taking up too much cabin space.

Seems like an easy question but in reality quite complicated.

Re the cost of new engines Bill you’re right.
And I’m not really sure about my original assumption used would not be too hard to find. Both engines would almost need to be low geared/big prop units. But one could always settle (or change his requirements to a single 30hp 4 cyl. I’d rather have twins if going to Alaska but looping w a single would probably be better.

Re keeping the old 8cyl engine one must consider the fact that the only way to make the boat more efficient is to reduce the boat weight or change the shape of the stern to a FD hull form. 120-150hp to cruise the 8cyl, 30hp for the OB versions or 18-20hp for the FD.

 

[Portage_Bay]

OP has said he's looking. Doesn't have a Catalina to convert, just thinking about the possibility.

His goal is under 30 ft, slow, economical on fuel and a budget of $25K.

With a tight budget I think it best to forego the bells n whistles. Stay basic and simple. Every creature comfort is a device or system to maintain which we all know takes $$$.

I briefly flirted with idea of trailerable boats not too many years ago. I stumbled across allweather boats. If he can find one, it might just fit the bill. https://allweatherboats.com/

At the time I thought I wanted simple, inexpensive and economical to run. But then I got bigger boat-itis.

 

[Benthic2]

Perhaps a compromise would be to find a boat with a bad 8 cyl and replace it with a 4 cyl....maybe from a low mileage car that was totalled ?

Is it possible that the outboards and reinforcement change the attitude of the boat so it is doing a permanent "wheelie" and the hulls is less efficient because the stern is lower in the water ?

 

[Nomad Willy]

Benthic2,
I would think doing an automotive conversion would be far more trouble than an OB. I’d leave that one alone. But a small marine diesel would be relatively easy to find thanks to sailboats. Very noisy tho. I’d go small gas if I could find one. May want to convert an IO engine ... convert it to straight shaft drive. One could go on the small size for the prop and reduce prop-walk.

Re your wheelie comment two 15hp OB’s on the wide end of the boat shouldn’t be a problem. Boat as per discussion is 9-10’ wide and w little deadrise.

 

[Solly]

Anybody want to talk about HP vs. fuel consumption ?? If the hull is a constant and it takes a certain amount of HP to move it at a fixed speed does it matter that much whether the HP comes from OB's, I/O's or inboard ??
Say 2 40 hp outboards. Your not going to run them wide open, say use 40 hp. between them. Would the inboard making 40 hp burn that much more fuel ??

 

[rslifkin]

Anybody want to talk about HP vs. fuel consumption ?? If the hull is a constant and it takes a certain amount of HP to move it at a fixed speed does it matter that much whether the HP comes from OB's, I/O's or inboard ??
Say 2 40 hp outboards. Your not going to run them wide open, say use 40 hp. between them. Would the inboard making 40 hp burn that much more fuel ??

It does matter somewhat. Different engine packages will show different efficiency at a given HP output. Gas engines in particular lose a lot of efficiency at low loads, so asking for 20hp from a 300hp engine is less efficient than 20hp from a 40hp engine. Different drive types may present different prop efficiency and different drag as well, altering the amount of HP needed.

 

[Nomad Willy]

Solly wrote;
“Anybody want to talk about HP vs. fuel consumption ?? If the hull is a constant and it takes a certain amount of HP to move it at a fixed speed does it matter that much whether the HP comes from OB's, I/O's or inboard ??
Say 2 40 hp outboards. Your not going to run them wide open, say use 40 hp. between them. Would the inboard making 40 hp burn that much more fuel ??”

Of course it matters.
But the OP is talking 6 (six) KNOTS.
This in not just an inboard to OB conversion.

For six knots w a much lighter boat only two 15hp OB’s will be required ... if my estimation is correct. And they will probably be run at about half throttle/load.

I have a good idea how much the OB’s will burn at 50% load. The inboard not so much. But it almost certainly be at idle or + a tad more. And if taken that route prop downsizing would almost be a given.

Don’t forget “six knots” as per the OP.

I’m still thinking a 30hp Honda (or whatever) single OB will work best for this boat at six knots.

 

[High Wire]

In NJ at least, just about every marina has a dozen dead boats sitting in the corner of the yard that have been abandoned. Take a look around and ask the marina your questions.

 

[Bill V]

I’m still thinking a 30hp Honda (or whatever) single OB will work best for this boat at six knots.

Couldn't agree more. For a beginner in boating a single is much less confusing then twin outboards and much less expensive to purchase used and maintain afterwards. Love the KISS principal.

Regarding automotive engine for use in boats. There are a few engines from cars and trucks that could be used, mostly V6 and V8's, but they would require purchasing heat exchangers and related water pumps for proper cooling plus changing the electrical/ignition to marine approved. For the most part I know of no 4 cylinder automotive engines that have been marinized in recent years and/or have marine exhaust manifolds available.