[PCW] Convert sail cat to power (another long one...)

[Candy Chapman and Gary Bell]

BTW gang, let's limit reposting my already overlong original posts in your replies by editing them down to relevant small edited bits with the delete key, and also delete the headings in reposted stuff...  I know my stuff is pretty glorious, but we only need to read it once, if that.  


Brian:
Gary had written:

> <>> If you want the PLANING hull type of power catamaran performance,
>> forget sail catamaran hulls unless you are willing to invest in
>> producing a hydrofoil supported boat with a proportionally huge
>> motor. It would probably be easier in such a case to start from
>> scratch.
> ________________________________________________
> ...your quote,"forget sail catamaran hulls unless you are willing to 
> invest
> in
> producing a hydrofoil supported boat"
>
> Brian replied:
> Not necessarily so, I have developed some ideas on this conversion of 
> sailing
> cat hulls to power cat forms with increased HP. This came about as a 
> result
> of
> my looking at a 50 foot project overseas, and a client's desire for 
> greater
> HP, and faster perf than the stock sailing hulls. 


Gary:
OK, watcha got?  I've pretty much showed my hand... ;-}  Everybody wants 
greater performance and greatly reduced costs.  The key difference 
between new and naive design clients and their designer is the training 
and experience needed to guide the client to practical and efficient 
choices in keeping with the depth of their wallets. 

> <>Brian:
> If you are not seeking this increased perf, then don't bother. 

Gary: 
Precisely.  The current run of sailing cats don't do badly under power 
alone.  If our hypothetical redesign client would simply leave the sail 
rig in place, and never unfurl anything as they merrily powered about, 
they would look  just like most of the sailing set, who seldom unfurl 
their sails either. 
<><>
Brian:
If you are, tell me specifically what vessel you have in mind, and what 
power you have in
mind.

Gary:
I think you missed the context for my previous hydrofoil statement (I 
just now recapitalized the word PLANING in my original posting which you 
cited above).  If one wants the heady speed of the narrow tunnel planing 
power catamarans to be provided in a converted sail cat hull, one would 
need to lift the entirely unsuitable hulls more or less out of the water 
by using lifting hydrofoils and very large motors.  Or perhaps wings and 
small rockets mounted on deck ;-}.

Otherwise I agree entirely with what you said. Of course is possible to 
design and build a conversion of a sail catamaran into a fairly fast 
power catamaran, although I strongly suspect that the costs of finally 
overcoming all the difficulties would certainly bring the price of the 
project well above the cost of a suitable new boat.  Limits of the hull 
internal space and dimensions will still limit the size and placement of 
larger and heavier engines. Don't forget to leave a little room for the 
poor sod who will be maintaining and repairing these engines -- higher 
performance engines seem to always need a good deal more maintenance and 
more frequent repair!  The external shape of the hull will adversely 
impact not only the speed through the water; it will present some real 
challenges adding adequate props and rudders as well. Perhaps a modified 
'sail drive' could be mounted in a nicely protected spot just aft of the 
centerboards, near the bottom of the rocker in the bottom shape, where 
the hulls are wider and the overall center of gravity issues best 
compromised, but that would raise heck with the interior accomodations 
and still leave a pronounced stern squat. New rudders aft with 
protective skegs could perhaps be fitted with horizontal wings, possibly 
articulated trim tab fashion to remedy the squatting or as powered 
stabilizers to eliminate some pitching motion as well. What PDQ found 
out when they built their prototype powercat based on their 32 foot 
sailing cat was that they really needed an entirely different bottom 
shape to accomodate these and a couple of other issues (stern squatting 
at speed, protecting props and rudders for the inevitable beachings cats 
do so well, etc.). I know this, as I advanced them funds -- in the form 
of a huge down payment -- specifically to allow them to finish the new 
molds and shift production from the initial modified 32 foot power hull 
to the fully redesigned 34.   One of the key modifications of this 
redesign was the additon of as much more flat bottom as possible from 
amidships aft, and particularly in the extended flat sections above and 
aft of the props.  Generally sail hulls feature very fine exits with 
high prismatic coeficients, and the initial redesign had replaced that 
with quite a bit of flat bottom already.  These extended flat bottoms 
replaced most of the remaining stern squat (now less than five degrees 
at full speed) with improved semi-displacement planing speed and 
performance.
------------------------------



In his next message Brian replied:
I hadn't gotten to all of my email yet, but I wanted to compliment Gary on
this submission It is a really good synopis of the subject of conversion.

Gary:
Thanks. Clearly I am giving serious consideration to doing this for 
myself.   I did leave out a whole bunch of stuff, like the difficulties 
adding an interior helm station to a sailboat and the minimalist 
electric systems generally found on them (thanks to Arild for pointing 
that one out).  How many of the potential buyers of such boats want to 
stand outside to drive all the time? The crummy visibility from the 
saloons of such boats, and the difficulties adding all that stuff to an 
already efficient and thoughtfully planned interior space pretty much 
rules that approach out. I guess that would leave enclosing part or all 
of the cockpit as a pilothouse. A wide pilothouse which still allowed 
for an open sail handling cockpit behind (or ahead of, or raised in the 
middle of!) it might work out well.  Hey!  That would yield the very 
catamaran motorsailer we discussed not so long ago!

Brian:
There may be one other consideration in larger vessel sizes. There are some
folks (and power folks in particular) who don't want to wait for a custom
boat build. Maybe they suddenly decided it is time to go cruising doing 
the coming
economic slump. They could be likely candidates for an 'upscale' sailing cat
with the rig removed (frightens some non-sailers)

Gary:
I suppose so. Which would be easier for them:  paying the very 
considerable costs in time and money of compensating for the 
incompatabilities between a fast power catamaran and the currently 
available sailing cat designs; accepting the already adequate speeds of 
existing powered sail cat performance (with or without the sail rig); or 
rather overcoming their anxiety about learning to sail, an activity many 
of us love and can practice well into our retirement years<>?  Given my 
notion that the cost of a successful, complex and neccessarilly complete 
conversion (you couldn't just do half the job) would likely far exceed 
the cost of a new or used contemporary power catamaran<> -- the sort of 
client you mentioned who didn't want to wait for a custom built power 
catamaran might be better advised to find a suitable new or used power 
cat and contemplate customizing it to meet their needs.  Such power 
catamarans are available to them right away -- although at considerably 
higher initial cost and much smaller availability.  Their final costs 
would be much lower, and they would not have to wait nearly so long for 
the modifications and remodifications to be worked out.  There are so 
many issues to be resolved in redesigning an existing sailing catamaran 
to provide planing power catamaran speeds, and these issues are 
guaranteed to interact with each other and with the remaining parts and 
performance of the boat in so many complex ways, that considerable time 
must be allowed to re-test, re-redesign and re-modify the initial 
redesigned prototype to provide even acceptable performance.  A good 
designer might well succeed in educating them about the various aspects 
of these issues and convince them to modify their initial wish list in 
favor of more practical, and quicker options.  My preference would still 
be for a boat which retains the sail rig and the existing tiny saildrive 
power plant, skipping the higher speeds under power alone.  I would 
capitalize on the modern roller furling and powered sail handling gear 
available today. Admittedly that might well not be acceptable for folks 
who are intimidated by their inexperience sailing, and for folks who 
aren't interested in the extended blue water passages that sail makes 
available.  Their loss, in my view.   

I am too old to indulge in worshiping the numbers:  Giant engines; huge 
horsepower; higher speeds and ever bigger boats.  I'm just not that 
insecure anymore. 

<><>I want to also point out that successful long term cruising is 
hardly compatable with full and tight schedules. If the schedule is more 
or less vague, then the journey trumps the destination, producing 
happiness and contentment. For my retirement cruising (in that spirit) I 
have little lust for high speeds at all, save outrunning unexpected 
heavy weather on a deepwater passage. In such a case there should be 
plenty of wind already available to achieve a fine turn of speed under 
sail alone, relieving the anxiety about digging too deeply into fuel 
reserves for an extended high speed run.  

This is fun...
Gary