Cruisers Forum
 


Reply
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 07-10-2020, 15:52   #1
Registered User

Join Date: Oct 2020
Posts: 4
Pearson 30 atomic 4 optimal rpm at hull speed?

Hi all, recently bought a 1977 Pearson 30 with a locked up atomic 4 that I've decided to scrap and replace with an electric motor. Unfortunately I'm not having much luck finding a particular spec:

Does anyone know what the optimal RPM that the atomic 4 is designed to run at in order at to achieve hull speed?

Thanks!!
Tackrun is offline   Reply With Quote
Old 07-10-2020, 16:29   #2
Registered User

Join Date: Aug 2020
Location: Hamlin, NY
Boat: O'Day 27
Posts: 58
Re: Pearson 30 atomic 4 optimal rpm at hull speed?

Quote:
Originally Posted by Tackrun View Post
Hi all, recently bought a 1977 Pearson 30 with a locked up atomic 4 that I've decided to scrap and replace with an electric motor. Unfortunately I'm not having much luck finding a particular spec:

Does anyone know what the optimal RPM that the atomic 4 is designed to run at in order at to achieve hull speed?

Thanks!!
This might be of interest. https://www.moyermarineforum.com/for...el+consumption
Joefiss is offline   Reply With Quote
Old 07-10-2020, 16:49   #3
Registered User
 
Svsumurun's Avatar

Join Date: May 2018
Location: Lake Erie
Boat: Pearson 365 ketch
Posts: 117
Re: Pearson 30 atomic 4 optimal rpm at hull speed?

Depends on the prop .... we had a P30 and it really didn't need much throttle to hit hull speed ( which, btw the boat could go WAY faster than that) .. 1500 rpm on ours would cruise at hull speed all day long..
Svsumurun is offline   Reply With Quote
Old 07-10-2020, 16:52   #4
Registered User

Join Date: Oct 2020
Posts: 4
Re: Pearson 30 atomic 4 optimal rpm at hull speed?

Awesome thank you!! Was yours a shaft drive with 2 blade prop?
Tackrun is offline   Reply With Quote
Old 07-10-2020, 17:16   #5
Registered User
 
Svsumurun's Avatar

Join Date: May 2018
Location: Lake Erie
Boat: Pearson 365 ketch
Posts: 117
Re: Pearson 30 atomic 4 optimal rpm at hull speed?

Yes it was
Svsumurun is offline   Reply With Quote
Old 07-10-2020, 17:32   #6
Registered User

Join Date: Oct 2020
Posts: 4
Re: Pearson 30 atomic 4 optimal rpm at hull speed?

One last thing if you don't mind - do you remember about what that max speed & rpm you could run was?
Tackrun is offline   Reply With Quote
Old 07-10-2020, 18:45   #7
Registered User

Join Date: Apr 2005
Location: ME, TCI, On da boat
Boat: Pearson 323, Tayana V42CC
Posts: 410
Images: 1
Re: Pearson 30 atomic 4 optimal rpm at hull speed?

You can not get a displacement hull to go faster than the hull speed which is determined by water line length. In the 77 pearson 30 it's 25'LWL and a hull speed of 6.7kts. You could pump 100HP through a prop and not go faster than 6.7kts. The more power you supply the more the stern will squat into the water.


RPM and speed will depend on the size and pitch of your prop.

https://www.westerbeke.com/advanced%...literature.pdf
Scubaseas is offline   Reply With Quote
Old 07-10-2020, 18:56   #8
Moderator
 
Jim Cate's Avatar

Join Date: May 2008
Location: cruising SW Pacific
Boat: Jon Sayer 1-off 46 ft fract rig sloop strip plank in W Red Cedar
Posts: 17,181
Re: Pearson 30 atomic 4 optimal rpm at hull speed?

IIRC most Anemic Four trannies were direct drive, ie no reduction in rpm from motor. As a result, most yachts with A-4s had rather small diameter props. If you are changing to an electric drive, it would behoove you to put a considerably larger diameter prop in service, for it will be far better in converting electrical energy into thrust.

Jim
__________________
Jim and Ann s/v Insatiable II, back in Port Cygnet after adventures in the big smoke.
Jim Cate is online now   Reply With Quote
Old 07-10-2020, 18:56   #9
Registered User

Join Date: Aug 2016
Location: Long Island, NY
Boat: Cal 33-2
Posts: 238
Re: Pearson 30 atomic 4 optimal rpm at hull speed?

Most A4s were direct drive. That means the prop turns much faster than ideal for best efficiency. A new power plant, electric or diesel, would allow for a slower turning, larger, and more efficient prop. You are really looking at clean sheet of paper. Don't focus too much on the A4 installation.
__________________
S/V First Tracks
1985 Cal 33-2
JimsCAL is offline   Reply With Quote
Old 07-10-2020, 20:09   #10
Moderator
 
Jim Cate's Avatar

Join Date: May 2008
Location: cruising SW Pacific
Boat: Jon Sayer 1-off 46 ft fract rig sloop strip plank in W Red Cedar
Posts: 17,181
Re: Pearson 30 atomic 4 optimal rpm at hull speed?

See above two posts for an example of synchronicity.

Jim
__________________
Jim and Ann s/v Insatiable II, back in Port Cygnet after adventures in the big smoke.
Jim Cate is online now   Reply With Quote
Old 08-10-2020, 08:30   #11
Senior Cruiser
 
GordMay's Avatar

Cruisers Forum Supporter

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 39,214
Images: 241
Re: Pearson 30 atomic 4 optimal rpm at hull speed?

From the
Atomic 4 OPERATION AND MAINTENANCE MANUAL
https://www.westerbeke.com/operator%...erator_man.pdf

Maximum RPM = 3500
Reduction Gear Ratio(s): 2:1(UJR), or 1:1, 1.29:1, 1.67:1, 2:1 (UJR VD)
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"



GordMay is online now   Reply With Quote
Old 08-10-2020, 08:48   #12
Registered User

Join Date: Mar 2015
Posts: 596
Re: Pearson 30 atomic 4 optimal rpm at hull speed?

Quote:
Originally Posted by Scubaseas View Post
You can not get a displacement hull to go faster than the hull speed which is determined by water line length. In the 77 pearson 30 it's 25'LWL and a hull speed of 6.7kts. You could pump 100HP through a prop and not go faster than 6.7kts. The more power you supply the more the stern will squat into the water.


RPM and speed will depend on the size and pitch of your prop.

https://www.westerbeke.com/advanced%...literature.pdf
perhaps you can explain why i've been able to exceed hull speed in my Pearson 10M? Even hitting 12 Knots one day. 29' waterline.
guyrj33 is offline   Reply With Quote
Old 08-10-2020, 09:50   #13
Registered User

Join Date: Apr 2005
Location: ME, TCI, On da boat
Boat: Pearson 323, Tayana V42CC
Posts: 410
Images: 1
Re: Pearson 30 atomic 4 optimal rpm at hull speed?

Quote:
Originally Posted by guyrj33 View Post
perhaps you can explain why i've been able to exceed hull speed in my Pearson 10M? Even hitting 12 Knots one day. 29' waterline.

Speed over ground or speed through water? 12 knots on a 28.3' water line is a remarkable statement. If you go faster than the wave you are making you are planing which is hard to do in a Pearson 30. Or a 10M for that matter. Getting a 10M to plane might be possible but I doubt you can get a P30 to do it.



I've hit 11 knots in my Pearson 323 but I had to be in a 5kt fair current to do it.



Look up "hull speed" on Wiki for a brief discussion.



If you have a boat with a 30hp motor and try upping it to 50hp it won't make the boat go any faster but it will push the hull down more into the water.
Scubaseas is offline   Reply With Quote
Old 08-10-2020, 10:04   #14
Registered User

Join Date: Mar 2015
Posts: 596
Re: Pearson 30 atomic 4 optimal rpm at hull speed?

Quote:
Originally Posted by Scubaseas View Post
Speed over ground or speed through water? 12 knots on a 28.3' water line is a remarkable statement. If you go faster than the wave you are making you are planing which is hard to do in a Pearson 30. Or a 10M for that matter. Getting a 10M to plane might be possible but I doubt you can get a P30 to do it.



I've hit 11 knots in my Pearson 323 but I had to be in a 5kt fair current to do it.



Look up "hull speed" on Wiki for a brief discussion.



If you have a boat with a 30hp motor and try upping it to 50hp it won't make the boat go any faster but it will push the hull down more into the water.
Iím referring to speed through the water, speed over ground has nothing to with hull speed discussions.
12 kt in a 10m is very exciting.
guyrj33 is offline   Reply With Quote
Old 08-10-2020, 10:44   #15
Registered User
 
thomm225's Avatar

Join Date: Aug 2011
Boat: B27
Posts: 6,927
Re: Pearson 30 atomic 4 optimal rpm at hull speed?

Quote:
Originally Posted by Tackrun View Post
Hi all, recently bought a 1977 Pearson 30 with a locked up atomic 4 that I've decided to scrap and replace with an electric motor. Unfortunately I'm not having much luck finding a particular spec:

Does anyone know what the optimal RPM that the atomic 4 is designed to run at in order at to achieve hull speed?

Thanks!!
Call Moyers Marine.

They know all about the Atomic 4 Engine

https://moyermarine.com/
thomm225 is offline   Reply With Quote
Reply

Tags
hull, hull speed, pearson, pearson 30, rpm

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
Hull Speed/RPM Ford Lehman Rodeo44 Engines and Propulsion Systems 8 15-03-2020 09:10
Spring Maintenance for Atomic 4 on Pearson 30 Sailon1 Engines and Propulsion Systems 1 13-02-2017 11:06
Fuel Economy of an Atomic 4 on a Pearson 30 Cest la Dave Engines and Propulsion Systems 9 09-01-2015 16:11
Carver 500 450 Cummins optimal cruise RPM jbooth10 Off Topic Forum 3 30-05-2013 12:38
Pearson 30 advice - considering purchase of 1973 boat with an Atomic 4 Donald Small Monohull Sailboats 4 14-06-2012 21:55

Advertise Here


All times are GMT -7. The time now is 03:36.


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.