Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 15-10-2012, 20:56   #1
Registered User

Join Date: Oct 2012
Location: On Gaiamar
Boat: Beneteau CC 42
Posts: 9
External Strainer Orientation

Greetings,

After reading many other threads I remain in need of knowledge and advise.

All 18 thru hulls have been replaced with new bronze. The problem is
that the contractor reversed the slotted strainers to face forward.
Original orientation was aft. Now they are glued and screwed in. There
were some words and now a standoff of wills.

The boat is a Beneteau 42CC and we sail at 6 or 7 kts. There are 3
external strainers 1 A/C (Not so worried here) 1 Gen and 1 Yanmar.

What is tha truth of the matter? Fore or aft.

Thanks Very Much
__________________

__________________
Gaiamar is offline   Reply With Quote
Old 15-10-2012, 21:06   #2
Marine Service Provider
 
Maine Sail's Avatar

Join Date: Jan 2007
Location: Maine
Boat: CS-36T - Cupecoy
Posts: 3,060
Re: External Strainer Orientation

Quote:
Originally Posted by Gaiamar View Post
Greetings,

After reading many other threads I remain in need of knowledge and advise.

All 18 thru hulls have been replaced with new bronze. The problem is
that the contractor reversed the slotted strainers to face forward.
Original orientation was aft. Now they are glued and screwed in. There
were some words and now a standoff of wills.

The boat is a Beneteau 42CC and we sail at 6 or 7 kts. There are 3
external strainers 1 A/C (Not so worried here) 1 Gen and 1 Yanmar.

What is tha truth of the matter? Fore or aft.

Thanks Very Much

Neither. Sailboats should ideally use round, hole type, non-directional strainers. Groco and others make them. However, if you already have them they should face aft otherwise you can run a risk of hydrolocking your engine. Facing them aft can create a vacuum on the impeller circuit and potentially shorten life but I have not personally seen any change in impeller life when they aim aft. When they aim forward however I have seen hydrolocked engines..
__________________

__________________
Marine How To Articles
Maine Sail is offline   Reply With Quote
Old 15-10-2012, 21:07   #3
Registered User
 
Dsanduril's Avatar

Join Date: Aug 2011
Location: South Pacific
Boat: Outremer 50S
Posts: 1,451
Re: External Strainer Orientation

I bet this has as many (and as strong) opinions as anchors

FWIW, ours face forward and have for 30+ years. Presumably on the theory that water gets pushed into the strainer when underway, but I can't recall a conscious decision at the time.
__________________
Dsanduril is offline   Reply With Quote
Old 15-10-2012, 21:15   #4
Registered User
 
Ziggy's Avatar

Join Date: Apr 2008
Location: U.S., Northeast
Boat: Contessa 32
Posts: 1,421
Images: 2
Re: External Strainer Orientation

Actually, I think external strainers are a bad idea altogether. Much better to have a strainer like this that you can clean out from the inside of the boat.

__________________
... He knows the chart is not the sea.
-- Philip Booth, Chart 1203
Ziggy is offline   Reply With Quote
Old 15-10-2012, 21:21   #5
Registered User

Join Date: Oct 2012
Location: On Gaiamar
Boat: Beneteau CC 42
Posts: 9
Re: External Strainer Orientation

I do have an internal strainer and siphon break. These however do not
provide peace of mind. So would a surveyor flag this as a problem?

Thanks
__________________
Gaiamar is offline   Reply With Quote
Old 15-10-2012, 21:42   #6
Marine Service Provider
 
Maine Sail's Avatar

Join Date: Jan 2007
Location: Maine
Boat: CS-36T - Cupecoy
Posts: 3,060
Re: External Strainer Orientation

Quote:
Originally Posted by Dsanduril View Post
I bet this has as many (and as strong) opinions as anchors
Pretty strong opinions from engine makers too. They bolded it and made it a boxed warning in the manual, not me...:


From Westerbeke / Universal

CAUTION: Do not use a high speed scoop-type
through-hull fitting for the raw water supply for
generators and auxiliary sailboat engines as it will tend to encourage siphoning. Water pressure against this type of fitting while the vessel is underway with the generator off or when sailing can push water past the raw water pump impeller and into the exhaust system, filling it and the engine as well.
__________________
Marine How To Articles
Maine Sail is offline   Reply With Quote
Old 15-10-2012, 22:53   #7
Senior Cruiser
 
delmarrey's Avatar

Cruisers Forum Supporter

Join Date: Mar 2003
Location: Now in Blaine, WA
Boat: Modified Choate 40
Posts: 10,702
Images: 122
Re: External Strainer Orientation

Power boats should face forward only, so when they go fast they don't loose suction in the air bubbles forced under the boat by speed or lift. Sailboats it doesn't matter too much but it's better facing aft to keep out the seagrass. Anchoring/docking is the worst time where one picks up junk out of the water.
__________________
Faithful are the Wounds of a Friend, but the Kisses of the Enemy are Deceitful! ........
A nation of sheep breeds a government of wolves!

Unprepared boaters, end up as floatsum!.......
delmarrey is offline   Reply With Quote
Old 16-10-2012, 00:38   #8
Senior Cruiser

Cruisers Forum Supporter

Join Date: Mar 2007
Location: Santa Cruz
Boat: Boatless Again
Posts: 4,324
Re: External Strainer Orientation

Can't figure out how to post a graph, but the dynamic head (how far above the static waterline that water will rise in a forward facing scoop) is 1.6 ft at 6 knots, and 4.4 ft at 10 knots. This neglects any wave effects.
__________________
donradcliffe is online now   Reply With Quote
Old 16-10-2012, 02:10   #9
Registered User
 
Ziggy's Avatar

Join Date: Apr 2008
Location: U.S., Northeast
Boat: Contessa 32
Posts: 1,421
Images: 2
Re: External Strainer Orientation

Quote:
Originally Posted by Gaiamar View Post
I do have an internal strainer and siphon break. These however do not provide peace of mind.
As far as I can tell, if you have an internal strainer, an external strainer can provide peace of mind but does not add any safety or serve any practical purpose.

An internal strainer basket can be cleared in a minute if it gets clogged. The only way to clear an external strainer is to go into the water.

You can get more peace of mind by removing the external strainer and fitting a tee to the seacock (with a plug in the straight up branch.) That way if the thruhull gets obstructed with some debris, you can remove the plug from the tee and poke an icepick or a screwdriver through the seacock and remove the obstruction.
__________________
... He knows the chart is not the sea.
-- Philip Booth, Chart 1203
Ziggy is offline   Reply With Quote
Old 16-10-2012, 11:19   #10
Marine Service Provider

Join Date: May 2012
Location: New Orleans
Boat: We have a problem... A serious addiction issue.
Posts: 3,940
Re: External Strainer Orientation

External strainers were a bad idea from the beginning, and scooped strainers have sadly been taken from the narrow realm they should be used in, to general purpose.

Scooped strainers are designed to be used on high speed power boats (over 70kn) to force water into the system, other than that narrow purpose they have no useful application on boats.
__________________
Greg

- If animals weren't meant to be eaten then they wouldn't be made of food.
Stumble is offline   Reply With Quote
Old 16-10-2012, 11:28   #11
Senior Cruiser
 
delmarrey's Avatar

Cruisers Forum Supporter

Join Date: Mar 2003
Location: Now in Blaine, WA
Boat: Modified Choate 40
Posts: 10,702
Images: 122
Re: External Strainer Orientation

Quote:
Originally Posted by Ziggy View Post
You can get more peace of mind by removing the external strainer and fitting a tee to the seacock (with a plug in the straight up branch.) That way if the thruhull gets obstructed with some debris, you can remove the plug from the tee and poke an icepick or a screwdriver through the seacock and remove the obstruction.
My sea strainer is removable with 4 screws for cleaning. But.......



.
Attached Thumbnails
Click image for larger version

Name:	motor_complete1.jpg
Views:	242
Size:	434.0 KB
ID:	48378   Click image for larger version

Name:	DSCN3702.JPG
Views:	247
Size:	70.7 KB
ID:	48379  

__________________
Faithful are the Wounds of a Friend, but the Kisses of the Enemy are Deceitful! ........
A nation of sheep breeds a government of wolves!

Unprepared boaters, end up as floatsum!.......
delmarrey is offline   Reply With Quote
Old 16-10-2012, 11:50   #12
Registered User

Join Date: Oct 2012
Location: On Gaiamar
Boat: Beneteau CC 42
Posts: 9
Re: External Strainer Orientation

I heard verbally that the ABYC standard indicates aft orientation. I'm
unable to confirm. Thanks for everybody's help with this issue.
__________________
Gaiamar is offline   Reply With Quote
Old 16-10-2012, 12:09   #13
Marine Service Provider
 
Maine Sail's Avatar

Join Date: Jan 2007
Location: Maine
Boat: CS-36T - Cupecoy
Posts: 3,060
Re: External Strainer Orientation

Quote:
Originally Posted by Gaiamar View Post
I heard verbally that the ABYC standard indicates aft orientation. I'm
unable to confirm. Thanks for everybody's help with this issue.

The ABYC defers to the manufacturers instructions on this. I gave you Westerbek/Universlal's stance here's Yanmar's:


Yanmar
"Scoop Strainer: Install the strainer so that the large area of the scoop strainer faces away from the direction of the ships forward movement, as shown in the figure."

Yanmar also want's it facing aft if using a "scoop" type strainer.
__________________
Marine How To Articles
Maine Sail is offline   Reply With Quote
Old 26-10-2012, 15:17   #14
Registered User

Join Date: Jul 2012
Location: Mallacoota - SE Australia
Boat: 1950's Lakes Cruiser
Posts: 82
Re: External Strainer Orientation

Thanks Main Sail, excellent information on how to install a seacock without drilling through the hull - I have a wooden boat - can I use hardwood instead of fibreglass as the backing plate ?? - Karl R
__________________
MV-Romnya is offline   Reply With Quote
Old 26-10-2012, 19:50   #15
Senior Cruiser
 
delmarrey's Avatar

Cruisers Forum Supporter

Join Date: Mar 2003
Location: Now in Blaine, WA
Boat: Modified Choate 40
Posts: 10,702
Images: 122
Re: External Strainer Orientation

Quote:
Originally Posted by MV-Romnya View Post
I have a wooden boat - can I use hardwood instead of fibreglass as the backing plate ?? - Karl R
What I have found that works really well is composite decking, like what's used for homes. It's PVC impregnated with wood fiber and feels, acts and looks like real wood but will not rot. It will crack if one tries to bend it too far but once it's epoxied down and covered with a coat of epoxy it works excellent. Screws go into it just like wood.

I used the TimberTech TF with excellent results. Check out my blog (Sealing the Hull to Deck Joint).


.
Attached Thumbnails
Click image for larger version

Name:	DSCN0213.jpg
Views:	154
Size:	402.4 KB
ID:	48837   Click image for larger version

Name:	DSCN0218.jpg
Views:	158
Size:	418.7 KB
ID:	48838  

Click image for larger version

Name:	DSCN0223.jpg
Views:	125
Size:	405.4 KB
ID:	48839  
__________________

__________________
Faithful are the Wounds of a Friend, but the Kisses of the Enemy are Deceitful! ........
A nation of sheep breeds a government of wolves!

Unprepared boaters, end up as floatsum!.......
delmarrey is offline   Reply With Quote
Reply

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




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 09:41.


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.