Unusual conversion project

Unusual conversion project.......outboard to diesel performance help

Hello.....I have a 1955 Skagit 20 cabin cruiser (fiberglass) , originally powered by a 35 HP outboard. Probably the largest available in those days. My guess is it probably cruised around 20-25 knots in that configuration.

It's now midway in a conversion to inboard v-drive and
I'm hoping someone here can provide estimates for what diesel would provide similar performance.

I figure I'll want 1:1 gears since cruising with something like a Yanmar will be around 3000 rpm.

This is a very light boat maybe 1000 lbs and almost no deadrise aft.

I'm new here.....is this the right forum?


Thanks,
Duncan

 

20' boats don't have a lot of room for stern drives or straight shaft inboards. Are you sure you want to occupy 40% of the cockpit with an engine box? Second, you'll pay dearly in excess weight with a diesel. Small outboard powered craft want and need to be light or preformance suffers. I'd be surprised if it was 1,000 pounds. In the mid 50's 'glass boats (for the most part) were ungodly heavy compared to a modern version of similar configuration. You's be lucky if it was under a ton. Your pictures are awfully small, but I can't see an outboard cutout. Has it been filled in and how?

 

There is no way a 20 foot boat with a 35HP will cruise at 25 knots. Pars weight estimate of one ton is generous. Add some people fuel and gear and it will double that. There were outboards of more power then. Also, if you plan on using an outboard of more than 35HP the steering can't be the cable and pulley system. You will need to put a new helm, etc.

 

Actually, I get 23 MPH with a 2,000 pound boat and a 35 HP engine. Gonzo has a point and cruising displacement will likely be in the 3,000 pound range, which assumes a well fed skipper, his trophy wife and equally well fed Fedel the wonder dog and a couple case of beer on ice, the fuel tanks full and typically equipped for a day on the local puddle. You could easily get much heavier then this. At 3,000 pounds the 35 HP now is only able to drag you to 19 MPH, which also assumes about 7% slip.

Now onto details, such as a 40 HP diesel, which will range, but is roughly in the 400 pound arena and a hell of site more then an outboard. This doesn't include strut, shaft, wheel and V drive, but does include a a typical transmission, such as a ZF2-3R.

 

conversion project

Wow.....tough crowd!
Here's a little more background:
I'm sixty years old and have been in the marine industry for most of my life. Back in the sixties I had a 17 foot drag boat, v-drive, small block Chevy, while the family boat was a 20' Skagit similar to this one.
This project is some weird attempt at reliving some of that in one vessel, I'm sure therapy would be cheaper but not as much fun.
It will be a toy and initially will have the same drive train as the drag boat....practicality isn't really in the equation at this time. At least initially.
I suspect after a season or two of roaring around at $100/hr, the thrill will wane and one option would be a little diesel, again like a little four cylinder turbo Yanmar, if it will plane with that. Anything larger will probably get prohibitively expensive.
I'm still confident this thing is light. I'm familiar with how heavily many fiberglass boats were built back in those days....it was still cutting edge and heavy was the safety factor. I briefly owned a Chinook 34 Hull #1 from 1954 and it was very heavily laid up and reinforced.
I think this Skagit is laid up entirely with cloth rather than any roving and the topsides are THIN. I'll have a more accurate weight shortly and may have to eat my words.
In any case, the transom has been glassed in and stringers installed for an inboard....so at this point, I'm committed or maybe should be

 

......project

The original brochure shows 1050 lbs.
I know "factory specs" aren't always reality based and there will be tanks and machinery but on the other hand, I'm going to begin dieting as an offset. (brochure attached)

 

Yanmar made a 35HP diesel outboard.

Should answer all the problems.

Bolt on a 50 or 100HP Honda till you go broke paying for speed , then install the diesel, for 2 gph fun.

FF

 

Yup lol, you need ear muffs on here!

I want the same info for my build - 32 ft trawler - pleasure use.
Anyway, seems I need to chose the donk first, then all else assumes it's position...

 

Your cockpit space will all but vanish with the inboard, what was wrong with staying with an outboard, a four stroke will be quite economical. The boat doesn't look terribly beamy, so loading it up with a heavy engine could turn it into a slug.

 

7' 6" of beam and a weird "exit" from the looks of it. Can you post pictures?

 

If you have your heart set on a diesel and want to relive hot rod days...a VW TDI of 90 or 110 hp is around 250 pounds complete-go buy a good used one for $1000 and figure out a trans.

That 40hp Yanmar you talk about is multitudes that price.

 

Inboard project

PAR, Here is a photo of the transom on a Skagit 20.

I've learned it took twin 35's back in the 50's to make one plane.

WestVanHan.....I like your VW TDI suggestion...at 250 lbs. that would be fun and economical. I'll do some research.

thanks guys!

 

P:

I'm sure it's CDK that was kind enough to start a whole thread on marinisation of the VW diesels.

Search the forum and you'll find it.

 

The exit looks much better then the brochure drawing above. I'm seeing a partial liner, furniture, plywood bulkheads, V berth, all for a just over a thousand pounds? I'll bet this is the raw hull shell weight. Full up, engine, tanks, etc. I'll bet a ton at the least, probably more, which also explains why twins 35's where needed to get it on plane. She looks to be a typical warped bottom of the era, which is a fairly easy hull shape to "get up" so it's surely fairly heavy.

 

The top photo in the brochure - is that Deception Pass???