Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 17-06-2019, 10:39   #31
Registered User

Join Date: Jan 2015
Posts: 390
Re: DIY Diesel Electric Catamaran drives Feasibility ???

Quote:
Originally Posted by valhalla360 View Post
I'm not a fan of the sillette drive, I've heard enough hassles with them on other Gemini's. Much prefer an outboard option and it will likely be cheaper than any of the other options.
Yes there are some issues but there is a reliable diesel engine and much of that could be avoided with proper maintenance
With the outboard now You have another problem
No alternator for charging batteries and hot water only with a propane water heater
__________________

__________________
Now or Never
warrior 90 is offline   Reply With Quote
Old 17-06-2019, 10:51   #32
Registered User

Join Date: Apr 2013
Posts: 7,808
Re: DIY Diesel Electric Catamaran drives Feasibility ???

Quote:
Originally Posted by warrior 90 View Post
Yes there are some issues but there is a reliable diesel engine and much of that could be avoided with proper maintenance
With the outboard now You have another problem
No alternator for charging batteries and hot water only with a propane water heater
Most people...particularly on cats use solar, so charging isn't a huge benefit. Plus we could easily pull start our outboard if the battery was dead.

Much simpler and cheaper to run the propane water heater than run the engine for an hour to heat up water.

With modern fuel injected outboards, you lose a good deal of the fuel efficiency advantage (compared to older outboards) and darn reliable.
__________________

valhalla360 is offline   Reply With Quote
Old 17-06-2019, 11:09   #33
Registered User

Join Date: Nov 2015
Posts: 354
Re: DIY Diesel Electric Catamaran drives Feasibility ???

Using a single u-joint in any offset shaft design is a basic engineering no-no. A single joint causes the shaft to speed up/slow down slightly during each revolution. Which means the prop is doing the same thing, but it has a lot of mass and can load the shaft cyclically, leading to fatigue failure. The shaft end should have another u-joint, and the prop raising system should be a parallelogram mechanism so the prop axis and transmission output are always in parallel, letting the second u-joint cancel the speed variations induced by the first uj. And a 14' x 1" shaft is going to be flexible, meaning it could start to whirl/whip as it rotates. Better (stiffer) would be a hollow shaft double the diameter say. These are probably what your engineering friend was hinting at.

Whether you do either electric or hydraulic systems you'll need to factor in loses from cable or fluid flow in hoses. Can be substantial as each requires long runs. Lot to be said for KISS principles in designing...
Dymaxion is offline   Reply With Quote
Old 18-06-2019, 07:37   #34
Registered User
 
NahanniV's Avatar

Join Date: Mar 2011
Location: Nova Scotia Canada
Boat: Wharram Tiki 46
Posts: 1,313
Re: DIY Diesel Electric Catamaran drives Feasibility ???

Quote:
Originally Posted by Dymaxion View Post
Using a single u-joint in any offset shaft design is a basic engineering no-no. A single joint causes the shaft to speed up/slow down slightly during each revolution. Which means the prop is doing the same thing, but it has a lot of mass and can load the shaft cyclically, leading to fatigue failure. The shaft end should have another u-joint, and the prop raising system should be a parallelogram mechanism so the prop axis and transmission output are always in parallel, letting the second u-joint cancel the speed variations induced by the first uj. And a 14' x 1" shaft is going to be flexible, meaning it could start to whirl/whip as it rotates. Better (stiffer) would be a hollow shaft double the diameter say. These are probably what your engineering friend was hinting at.
...
Thanks for your input.

Yes, two U-joints at right angles or a CV-joint would be used in a replacement drive leg.

Do the shafts need to be parallel ? I thought it would be OK as long as the angles of the two U-joints are equal ?

The existing design tries to control whip with an outer aluminum tube that has hard plastic bearings inside.

A larger hollow shaft is an interesting idea, perhaps I could eliminate the outer aluminum tube. Is this ever done in marine applications ? Might be difficult to get it straight, and also connect to a prop ?
__________________
Cheers,
JM
nahannivatsea.blogspot.ca
NahanniV is offline   Reply With Quote
Old 18-06-2019, 07:59   #35
Registered User
 
NahanniV's Avatar

Join Date: Mar 2011
Location: Nova Scotia Canada
Boat: Wharram Tiki 46
Posts: 1,313
Re: DIY Diesel Electric Catamaran drives Feasibility ???

I started a new thread specifically about re-engineering the drive leg:

Help me re-engineer my Catamaran lifting drive leg - Cruisers & Sailing Forums
__________________
Cheers,
JM
nahannivatsea.blogspot.ca
NahanniV is offline   Reply With Quote
Old 18-06-2019, 08:42   #36
Registered User

Join Date: Jan 2015
Posts: 390
Re: DIY Diesel Electric Catamaran drives Feasibility ???

Quote:
Originally Posted by valhalla360 View Post
Most people...particularly on cats use solar, so charging isn't a huge benefit. Plus we could easily pull start our outboard if the battery was dead.


Much simpler and cheaper to run the propane water heater than run the engine for an hour to heat up water.


With modern fuel injected outboards, you lose a good deal of the fuel efficiency advantage (compared to older outboards) and darn reliable.
I donīt like dead batteries. They are expensive.
If You have an insulated water heater hot water is free.
Diesel engines are more efficient and more reliable then gas engines.

With todays fuel blends I absolutely donīt trust any outboard motors for my main propulsion.
__________________
Now or Never
warrior 90 is offline   Reply With Quote
Old 19-06-2019, 08:19   #37
Registered User

Join Date: Apr 2013
Posts: 7,808
Re: DIY Diesel Electric Catamaran drives Feasibility ???

Quote:
Originally Posted by warrior 90 View Post
I donīt like dead batteries. They are expensive.
If You have an insulated water heater hot water is free.
Diesel engines are more efficient and more reliable then gas engines.

With todays fuel blends I absolutely donīt trust any outboard motors for my main propulsion.
Who does like dead batteries? A properly sized and installed solar system is less likely to result in dead batteries. In fact, most engine charging never gets lead-acid up to 100% as you would have to run the engine for many hours. With solar, it's quite feasible to hit 100% a few times a week...which is good for batteries.

If you are referring to being able to pull start, that's a backup option. While it's possible to hand start diesels, none are nearly as easy as just grabbing the pull cord and giving it a couple yanks.

Running the diesel just to make hot water...no thanks.

Diesels have a slight edge in efficiency but with modern 4 stroke fuel injected, its not nearly as big of a difference like it was 30yr ago.

Never had an issue with our 25hp EFI being reliable or issues with fuel. Only problem we ran into is a couple times after we first got it, I thought it stalled since it was so quiet and hit the starter with it running for a second before realizing, it was already running.
__________________

valhalla360 is offline   Reply With Quote
Reply

Tags
catamaran, diesel, DIY, electric

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Sail Drives VS direct drives LLizzard Multihull Sailboats 87 21-02-2017 23:15
feasibility of variable length hull/variable beam cat... black_sails Multihull Sailboats 15 04-05-2016 08:11
Feasibility of an Atlantic Circuit on a very short Sabbatical? Dockhead Atlantic & the Caribbean 29 03-12-2012 17:54
Question About Feasibility Star Journey Monohull Sailboats 0 12-07-2010 14:57
Sail-Drives or Shaft Drives? RubyBishop Multihull Sailboats 24 07-09-2009 09:14

Advertise Here


All times are GMT -7. The time now is 01:38.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2020, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.