[Engines] Determining proper HP for a given boat design. - SailNet Community

   Search Sailnet:

 forums  store  


Quick Menu
Forums           
Articles          
Galleries        
Boat Reviews  
Classifieds     
Search SailNet 
Boat Search (new)

Shop the
SailNet Store
Anchor Locker
Boatbuilding & Repair
Charts
Clothing
Electrical
Electronics
Engine
Hatches and Portlights
Interior And Galley
Maintenance
Marine Electronics
Navigation
Other Items
Plumbing and Pumps
Rigging
Safety
Sailing Hardware
Trailer & Watersports
Clearance Items

Advertise Here






Go Back   SailNet Community > On Board > Gear & Maintenance
 Not a Member? 
  #1  
Old 10-31-2007
Valiente's Avatar
Senior Member
 
Join Date: Jun 2006
Location: Toronto
Posts: 5,491
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 10
Valiente has a spectacular aura about Valiente has a spectacular aura about
[Engines] Determining proper HP for a given boat design.

A good friend of mine has a steel 36,000 lb. Goderich 40, a Bill Wallstrom design from the late '70s. Four of them were built. His original and underpowered for the job Volvo 35 HP is coming out and he is proposing putting in a Yanmar 75 HP turbo.

What he has asked me to find out is if anyone knows of some sort of Web resource that can properly match an "ideal" engine to a specific type of boat, given the usual designer's parameters, keel type, displacement, etc. He is thinking of going with the 75 to turn alternators, PTO for compressor, etc. and simply to have "extra" to push his three blade Autoprop that his old Volvo didn't have (although it could push him well enough at hull speed in flat water).

Does anyone know of websites with data along these lines? He could probably live with a 60 HP, but the price difference between a Yanmar 50 and a 75 is only a couple of grand.
Reply With Quote Share with Facebook
  #2  
Old 10-31-2007
.
 
Join Date: Nov 2006
Posts: 10,855
Thanks: 0
Thanked 3 Times in 2 Posts
Rep Power: 12
Giulietta is just really nice Giulietta is just really nice Giulietta is just really nice Giulietta is just really nice Giulietta is just really nice
Val, if he calls Yanmar with the boat's detail, they'll calculate it for free for him.

If they don't let me know I ask Pinto, my yanmar/crew/friend dealer and he will calculate it for you
Reply With Quote Share with Facebook
  #3  
Old 10-31-2007
Member
 
Join Date: Nov 2006
Location: Beacon, New York
Posts: 652
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 8
Tartan34C will become famous soon enough
Itís not the kind of thing that is solved with a simple individual formula so a webpage approach is unlikely and I donít know of any website that tries it. Is he mathematically inclined? If he is I can recommend some books that deal with this or point him to a collection of formulas.
All the best,
Robert Gainer
__________________
Study the history of naval architecture and move forward knowing what didnít work before.

Donít waste time making the same old mistakes but instead make new ones and to insure your place in history be sure the mistakes are big ones.

Never design a mast that is weaker then the boat
Never design a boat that is weaker then the mast

Never listen to someone describe why your project will not work unless they can show you the broken pieces of their own version.
Reply With Quote Share with Facebook
  #4  
Old 10-31-2007
JohnRPollard's Avatar
Moderator
 
Join Date: Mar 2007
Location: Chesapeake
Posts: 5,680
Thanks: 0
Thanked 2 Times in 2 Posts
Rep Power: 10
JohnRPollard is a jewel in the rough JohnRPollard is a jewel in the rough JohnRPollard is a jewel in the rough
Valiente,


Your friend might poke around here a bit:

http://boatdiesel.com/index.cfm?cfapp=31

I'm not certain, but one of the formulas he may be looking for might be called the "propeller exponent."

Nigel Calder did a nice article in this month's (OCT) Ocean Navigator -- entitled "Improving Low Speed Efficiency " -- which dealt in part with engine size selection. From the stand point of fuel consumption and efficiency, I was surprised at the magnitude of the penalty for going with TOO LARGE of an engine. So that "couple grand" price spread between the 60 and 75 would continue to grow over the life of the engine. Plus, without additional tankage, the range of the boat under power would go down.

So many variables...
Reply With Quote Share with Facebook
  #5  
Old 10-31-2007
Valiente's Avatar
Senior Member
 
Join Date: Jun 2006
Location: Toronto
Posts: 5,491
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 10
Valiente has a spectacular aura about Valiente has a spectacular aura about
Quote:
Originally Posted by JohnRPollard View Post
Valiente,


Your friend might poke around here a bit:

http://boatdiesel.com/index.cfm?cfapp=31

I'm not certain, but one of the formulas he may be looking for might be called the "propeller exponent."

Nigel Calder did a nice article in this month's (OCT) Ocean Navigator -- entitled "Improving Low Speed Efficiency " -- which dealt in part with engine size selection. From the stand point of fuel consumption and efficiency, I was surprised at the magnitude of the penalty for going with TOO LARGE of an engine. So that "couple grand" price spread between the 60 and 75 would continue to grow over the life of the engine. Plus, without additional tankage, the range of the boat under power would go down.

So many variables...
I'll check that out, thanks...I am expecting my copy of ON very soon.

That's exactly the sort of thing we were discussing, because his Autoprop was (even with a DriveSaver) very hard on the old Volvo, wearing out cones in the transmission and such, but the opposite is true, of course, that he might "lug" with too large an engine that he never gets into the proper power band.

This is why I decided to stick with my 52 HP, despite my 30,000 weight: with a four-blade VariProp, I will have a great deal of torque at low speeds, but I should be able to push the engine a little harder if I need speed. Right now with a fixed 18 x 13 three-blade, I can get to 6.4 knots at 2,100 rpm. With a four-blade 19 x 15 (the new prop), I suspect I'll run 200 rpm faster, which will be more efficient.
Reply With Quote Share with Facebook
  #6  
Old 11-01-2007
Senior Member
 
Join Date: Sep 2006
Posts: 2,194
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 8
Rockter will become famous soon enough
I am wary of turbos. Do we need them. Is the weight penalty of a normally aspirated engine really that bad?
Reply With Quote Share with Facebook
  #7  
Old 11-01-2007
Senior Member
 
Join Date: Jun 2004
Location: Malaysia
Posts: 314
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 11
haffiman37 is on a distinguished road
Quote:
Originally Posted by Rockter View Post
I am wary of turbos. Do we need them. Is the weight penalty of a normally aspirated engine really that bad?
I totally agree.
This seems to be an application where torque is more a question than speed and horsepower (Torque x rpm) and wheight not the biggest problem. Then it might get down to engine room size, what is room to put in, but I would have chosen and 'old' normally aspirated (non turbo) engine.
Reply With Quote Share with Facebook
  #8  
Old 11-01-2007
Valiente's Avatar
Senior Member
 
Join Date: Jun 2006
Location: Toronto
Posts: 5,491
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 10
Valiente has a spectacular aura about Valiente has a spectacular aura about
Quote:
Originally Posted by Rockter View Post
I am wary of turbos. Do we need them. Is the weight penalty of a normally aspirated engine really that bad?
Yeah, I've been making the same comments to him. Added mechanical complexity to what end? He already has excellent engine room ventilation, and it's a steel full-keeler...I've been hinting that maybe the Cummins 66 HP is a better choice, but he's saying that Yanmar is so widespread he'll never have to search for parts.

I think turbo is great for race boats where every gram counts, but both he and I are far less affected by 100 kilos in the engine bay than most, 100 kilos being 0.3% of our total displacement.
Reply With Quote Share with Facebook
  #9  
Old 11-01-2007
sailingdog's Avatar
Telstar 28
 
Join Date: Mar 2006
Location: New England
Posts: 43,291
Thanks: 0
Thanked 9 Times in 9 Posts
Rep Power: 13
sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice
Turbos aren't really an ideal solution for a marine application IMHO. To really benefit from a turbo, you need to open the throttle up more... and that is pretty hard on a marine use diesel. A better approach is generally to get a properly sized normally aspirated engine. It will be a bit heavier and larger, but it will also last longer IMHO.
__________________
Sailingdog

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Telstar 28
New England

You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

óCpt. Mal Reynolds, Serenity (edited)

If you're new to the Sailnet Forums... please read this
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
.

StillóDON'T READ THAT POST AGAIN.
Reply With Quote Share with Facebook
  #10  
Old 11-01-2007
RandyonR3's Avatar
Cruising
 
Join Date: Oct 2005
Location: crusing
Posts: 146
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 9
RandyonR3 is on a distinguished road
INHO..The turbo is an excelant choice for a sailboat.. been working woth turbos for a number of years, and installed one on every vehicle I owned .. its a sorce for un-used eneregy.
A turbo is, as we all know, are advetised as a performance add-on for most cars, but turbos have been used for truck applications all the way back to the 30s & 40s.. Its a sorce for tapping into power at LOW RPM as well as High..
On a boat, the ability to run a couple extra degrees of pitch while still operating at the same RPM or even lower and still keeping the same speed would be a positive swap..
On a desplacement boat...Catch the word "displacement" your pushing water, and that takes power.. and if you can create more power with less motor, thats a savings...
And what I've heard, the new Yanmar with a turbo, it only weeps fuel.
and the cost of fuel is getting higher every day,
I would change mine out in a minute, if this old war-horse would ever give out... I've got a perkins 4108 and the new yanmar is a perfect swap but with this Perkins, It will probably be here long after I'm gone..
Reply With Quote Share with Facebook
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

 
Posting Rules
You may post new threads
You may post replies
You may post attachments
You may edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On


Similar Threads
Thread Thread Starter Forum Replies Last Post
The legacy of Philip Rhodes GoodOldBoat Good Old Boat 25 12-14-2012 07:34 PM
What can you tell from the numbers? brazilnut Boat Review and Purchase Forum 10 07-01-2009 04:09 PM
Naming and Renaming Your Boat Sue & Larry Buying a Boat Articles 0 12-15-2003 07:00 PM
Understanding the Racing Rules, Part Three Dean Brenner Racing Articles 0 09-09-2002 08:00 PM
buying first boat jerrycooper14 Boat Review and Purchase Forum 21 04-23-2002 02:15 PM


All times are GMT -4. The time now is 11:58 AM.

Add to My Yahoo!         
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.1
(c) Marine.com LLC 2000-2012

The SailNet.com store is owned and operated by a company independent of the SailNet.com forum. You are now leaving the SailNet forum. Click OK to continue or Cancel to return to the SailNet forum.