Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 19-08-2009, 03:02   #1
Registered User
 
Jim Mc's Avatar

Join Date: May 2009
Location: aus
Boat: S&S 30
Posts: 48
Images: 2
Yanmar Single or Twin 12hp?

Would a single 12 hp have less grunt pushing a 4.5 ton yacht against a 3-4 knt tide than a twin 12hp? Thank you in advance ! I need advice!

Regards Jim
__________________

__________________
Jim Mc is offline   Reply With Quote
Old 19-08-2009, 04:47   #2
Senior Cruiser
 
Talbot's Avatar

Cruisers Forum Supporter

Join Date: Jun 2004
Location: Brighton, UK
Boat: Privilege 37
Posts: 3,579
Images: 32
against tide - probably marginal as you are looking there at boat speed through water so the tide is irrelevant.

against wind/waves - It may well make a significant difference, because a 2 cylider engine is likely to deliver more torque than the single cylinder, and thus be able to deliver the full revs.
__________________

__________________
"Be wary of strong drink. It can make you shoot at tax collectors - and miss."
Robert A Heinlein
Talbot is offline   Reply With Quote
Old 19-08-2009, 05:42   #3
Registered User
 
Jim Mc's Avatar

Join Date: May 2009
Location: aus
Boat: S&S 30
Posts: 48
Images: 2
Thanks Talbot, its times like this I wish I had trained in motor mechanics ! Thankyou for your time!
Regards Jim
__________________
Jim Mc is offline   Reply With Quote
Old 19-08-2009, 07:34   #4
Sponsoring Vendor
 
Tellie's Avatar

Community Sponsor

Join Date: Oct 2007
Location: Hollywood, Fl.
Boat: FP Athena 38' Poerava
Posts: 3,043
Just curious Jim Mc, what is the model of the Yanmar two cylinder 12 hp?
Tellie is offline   Reply With Quote
Old 19-08-2009, 08:51   #5
Moderator Emeritus
 
Ex-Calif's Avatar

Cruisers Forum Supporter

Join Date: May 2007
Location: Singapore
Boat: Maxi 77 - Relax Lah!
Posts: 11,514
Images: 4
This has a bit to do with "gearing" as well.

The weight of the boat will factor in when trying to accelerate the hull. The waterline length will set the theoretical hull speed.

When beating against wind, tide and swell the boat will be set back by each element.

You don't state hull length but if it's less than 28 your 12 hp will push it along at hull speed.

A higher revving engine, and lower pitch prop will help the boat accelerate into each swell or reaquire boat speed at the top of the swell.

I don't quite get your choice here. If you are looking at a multi and are thinking one 12hp vs twin 12hp, I would discuss more.

I am not a cat guy but I understand that many will motor or motorsail on one engine only in good conditions. The second engine also provides redundancy and safety factor.

I personally do not plan to have a cat with anything less than twin inboard powerplants. There are lots of reasons that pods, outboards and other options are viable but for all my personal reasons I choose the former.
__________________
Relax Lah! is For Sale <--- Click
Click--> Custom CF Google Search or CF Rules
You're gonna need a bigger boat... - Martin Brody
Ex-Calif is offline   Reply With Quote
Old 19-08-2009, 09:01   #6
Sponsoring Vendor
 
Tellie's Avatar

Community Sponsor

Join Date: Oct 2007
Location: Hollywood, Fl.
Boat: FP Athena 38' Poerava
Posts: 3,043
I'm curious if Jim has the choice in a twin why not go with the 18hp model? Would be a no brainer for me.
I didn't know Yanmar made a two cylinder 12hp.
Tellie is offline   Reply With Quote
Old 20-08-2009, 04:30   #7
Registered User
 
Jim Mc's Avatar

Join Date: May 2009
Location: aus
Boat: S&S 30
Posts: 48
Images: 2
Quote:
Originally Posted by Tellie View Post
I'm curious if Jim has the choice in a twin why not go with the 18hp model? Would be a no brainer for me.
I didn't know Yanmar made a two cylinder 12hp.
Thanks, ex calif and Tellie , I am looking at 30 footers [one hull] .I have seen one that is ok but it has a SVE12 yanmar [single]. I am concerned it wont give me the power needed to put me in position in the 3-4 knott cross tide in and out of the marina. as well as other situations like you metioned . Some other cadidates have small twins 12-15 hp .
[ not a particular model Tellie, sorry i was generalising]

It may be a case of find a boat that ticks most other boxes and put a suitable engine in it later. Very hard to find perfect boat

I suppose my question should have been how much less power would the SVE12 have in critical situations compared to a small twin say 12-15 hp?

Thanks again folks,

Regards Jim
__________________
Jim Mc is offline   Reply With Quote
Old 20-08-2009, 06:36   #8
Sponsoring Vendor
 
Tellie's Avatar

Community Sponsor

Join Date: Oct 2007
Location: Hollywood, Fl.
Boat: FP Athena 38' Poerava
Posts: 3,043
Quote:
Originally Posted by Jim Mc View Post
Thanks, ex calif and Tellie , I am looking at 30 footers [one hull] .I have seen one that is ok but it has a SVE12 yanmar [single]. I am concerned it wont give me the power needed to put me in position in the 3-4 knott cross tide in and out of the marina. as well as other situations like you metioned . Some other cadidates have small twins 12-15 hp .
[ not a particular model Tellie, sorry i was generalising]

It may be a case of find a boat that ticks most other boxes and put a suitable engine in it later. Very hard to find perfect boat

I suppose my question should have been how much less power would the SVE12 have in critical situations compared to a small twin say 12-15 hp?

Thanks again folks,

Regards Jim

Hi Jim, If you're considering a new two cylinder Yanmar you'd be looking at a 2GM20F. They are 18hp. If you wanted to replace the Yanmar with a new one cylinder it would be the 1GM10 which is only a 9hp motor. When you are talking engines this small I don't think worring about overpowering a boat is an issue. If it were me and I was repowering in this range I'd look at the most HP I could get. Yanmars 18hp over their old SVE12hp or the new 9hp again is a no brainer. As I see it, your options with Yanmars is either you rebuild the SVE when needed, because Yanmar doesn't make this model any more, I believe they were only produced between 1974 -1976. Or go with a new 2GM20F. For perhaps a few thousand saved up front on a rebuild, I'd go with the new 18hp instead. These things if properly taken care of will last you a long long time.
Tellie is offline   Reply With Quote
Old 20-08-2009, 14:12   #9
Registered User

Join Date: Jun 2009
Posts: 4
Yanmar no longer sells the 2GM20F due to emission requirements. They offer a smaller 2 cylinder, 14hp 2YM15 and a 3 cylinder, 21hp 3YM20 that is close in size to the 2GM20F. Specs are available on their website.
__________________
pdm26 is offline   Reply With Quote
Old 20-08-2009, 14:17   #10
Sponsoring Vendor
 
Tellie's Avatar

Community Sponsor

Join Date: Oct 2007
Location: Hollywood, Fl.
Boat: FP Athena 38' Poerava
Posts: 3,043
Quote:
Originally Posted by pdm26 View Post
Yanmar no longer sells the 2GM20F due to emission requirements. They offer a smaller 2 cylinder, 14hp 2YM15 and a 3 cylinder, 21hp 3YM20 that is close in size to the 2GM20F. Specs are available on their website.
Thanks for the update.
Tellie is offline   Reply With Quote
Old 20-08-2009, 14:18   #11
Senior Cruiser
 
Cheechako's Avatar

Cruisers Forum Supporter

Join Date: Aug 2006
Location: Skagit City, WA
Posts: 19,334
One consideration is the old Yanmar single was a very rough idling and vibration prone engine. Not very pleasant... two cyls would be smoother. I built a fairly heavy 31 footer once with a 13hp Volvo and it would make hull speed in flat water but generally was pretty underpowered....
__________________
Cheechako is offline   Reply With Quote
Old 20-08-2009, 15:11   #12
Registered User
 
Solitude's Avatar

Join Date: Nov 2008
Location: West Coast, BC , Canada
Boat: Cascade
Posts: 595
I have a Yanmar 1GM10 on my 27 at 6000lbs

I would sugest a 2 cyl model over a single for the vibration and noise. I believe you should look at sizing of 1 HP for every 500 lb.

Its not the current thats the problem as you won't do more than hullspeed anyway. Its the wind. I have no problem making hullspeed when its flat and calm but with a strong headwind (when I cant sail) it would be nice to have the extra hp. If your looking at 30 footers you need to be looking higher than 12hp or you will feel underpowered.
__________________
Solitude is offline   Reply With Quote
Old 20-08-2009, 15:27   #13
Moderator Emeritus
 
David M's Avatar

Cruisers Forum Supporter

Join Date: Sep 2007
Location: San Francisco Bay
Boat: research vessel
Posts: 10,150
Current is irrelevant. Current is the water speed with respect to the bottom. You're boat only "knows" of its speed through the water. Torque is a useless figure without speed...and that determines power. You can have a ten thousand foot-pounds of torque on a propeller that turns one RPM...and you will still have very little horsepower.

You wont notice any difference between a one or two cylinder, 12 horsepower engine because the power is directly and linearly converted to forward force..and that is what makes it move. If the prop is sized properly your engine will be able to reach the RPM at which 12 horsepower is generated. Power is power.
__________________
David

Life begins where land ends.
David M is offline   Reply With Quote
Old 20-08-2009, 15:59   #14
Moderator
 
Boracay's Avatar

Cruisers Forum Supporter

Join Date: Feb 2004
Location: Pelican Bay, Great Sandy National Park
Boat: Steel Roberts Offshore 44
Posts: 5,175
Images: 18
Don't do as I do...

I built a 7 tonne Hartley RORC 32 a few years ago and put a 7hp hand start in it.

The hand start can make things very simple. The small Yanmar looks to be be hand startable.

That engine would push the boat to 5 knots easy, maybe more under good conditions (getting old, memory hazy).

It was fine round Sydney Harbour with a few crew, and for short trips up the coast.

But now, looking at cruising short handed and over long distances, I went for a 85hp John Deere. Nice to have lots of power.
__________________
Rust never sleeps
Boracay Blog.
Boracay is offline   Reply With Quote
Old 20-08-2009, 23:19   #15
Moderator Emeritus
 
Ex-Calif's Avatar

Cruisers Forum Supporter

Join Date: May 2007
Location: Singapore
Boat: Maxi 77 - Relax Lah!
Posts: 11,514
Images: 4
I tried to hand start our Volvo MD2010 - Forget it!

In regard to 30 footers.

Just to push the boat around in and out of the slip 12hp would be fine. These days people seem to want more oomph in terms of acceleration - If I had to I'd go with 12 but I'd be happier with 15-18 and a properly sized prop especially for a heavier boat.
__________________

__________________
Relax Lah! is For Sale <--- Click
Click--> Custom CF Google Search or CF Rules
You're gonna need a bigger boat... - Martin Brody
Ex-Calif is offline   Reply With Quote
Reply

Tags
yanmar

Thread Tools
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
Twin Vee Dinghy? Ocean Roads Auxiliary Equipment & Dinghy 8 01-05-2009 09:57
Twin Alternators privileged Electrical: Batteries, Generators & Solar 2 21-04-2009 17:24
Center board vs keel vs twin keel vs twin centerboard jscott Monohull Sailboats 32 26-03-2009 15:48
Twin props Moby Dick Propellers & Drive Systems 21 12-06-2007 08:27
Single vs twin on cats vilanomark Multihull Sailboats 17 13-11-2006 21:26



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 17:24.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.