Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 26-05-2016, 11:22   #1
Registered User

Join Date: Feb 2011
Location: Eastern Mediterranean
Posts: 30
Bowsprit length vs. exact centerline?

I'm installing a Seldén bow sprit and have to choose the length to cut it (or not cut at all).

I'm wondering how important it is that the tack is exactly in the center line of the boat or if 5 to 10 cm (2-4") off center (32' boat) would be noticeable or a problem when sailing. If it's not a big deal I could make the bow sprit longer, which I would see as an advantage.

What I'm talking about is well within the load limits of the manufacturer, so no stability problem.

What do you think?
__________________

__________________
Copprhead is offline   Reply With Quote
Old 26-05-2016, 11:58   #2
Marine Service Provider

Join Date: May 2012
Location: New Orleans
Boat: We have a problem... A serious addiction issue.
Posts: 3,940
Re: Bowsprit length vs. exact centerline?

A non-center line sprint will be marginally better on one jibe, and substantially worse on the other. My guess is that for every degree above center line you get the sprint you can sail that much deeper (I know this to be true), but for every degree below center line it is you have to sail two degrees higher (guessing).

If it is at all possible to centerline the tack you really need to do so.
__________________

__________________
Greg

- If animals weren't meant to be eaten then they wouldn't be made of food.
Stumble is offline   Reply With Quote
Old 26-05-2016, 12:47   #3
Senior Cruiser

Cruisers Forum Supporter

Join Date: Aug 2009
Location: between the devil and the deep blue sea
Boat: a sailing boat
Posts: 17,314
Re: Bowsprit length vs. exact centerline?

Can be both on or off center depending on what sail you are flying. Longer may be better or not.

Some boats have bowsprits that can be 'gybed' from side to side. This is very nice if you are flying an older style gennaker running. You can push the sail to the windward thus. Not required with modern gennakers that can be built to float the top to windward.

Upwind, a small offset will not hurt by a bigger one will affect your tacking angles.

b.
__________________
barnakiel is offline   Reply With Quote
Old 26-05-2016, 13:57   #4
Registered User

Join Date: Feb 2011
Location: Eastern Mediterranean
Posts: 30
Re: Bowsprit length vs. exact centerline?

Thanks for your answers. The sail is a full radial / modern gennaker and i won't gybe the bow sprit, it can only be in one in and one out position.

barnakiel: could you elaborate on "Longer may be better or not."?

The boat has a gennaker option you can get from the yard, featuring the same bow sprit and a bracket/ring that is a bit different from mine, which is custom made so that the bow sprit doesn't collide with my anchor's roll bar. This way, the angle of the sprit is a bit different, and if I use the yard option length of sprit, the tack is about 8cm to starboard. I'd have to make it about 20 cm shorter to have the tack in the center. That would be about 10% shorter than the yard option.
__________________
Copprhead is offline   Reply With Quote
Old 26-05-2016, 15:14   #5
Senior Cruiser

Cruisers Forum Supporter

Join Date: Aug 2009
Location: between the devil and the deep blue sea
Boat: a sailing boat
Posts: 17,314
Re: Bowsprit length vs. exact centerline?

Sail geometry.

If your sail is built for geometry XYZ, it may work less efficiently on geometry XYZ'.

I think Z' is called J in sailmakers lore.

Maybe now you can expand on why you say longer may be better.

b.
__________________
barnakiel is offline   Reply With Quote
Old 26-05-2016, 17:49   #6
Marine Service Provider

Join Date: May 2012
Location: New Orleans
Boat: We have a problem... A serious addiction issue.
Posts: 3,940
Re: Bowsprit length vs. exact centerline?

A longer sprint is always better, assuming the sail is cut to fit. There may be a point at which that fails, but up to at least 3 time the J length it's true. The advantage is that the sail gets out of the shadow of the main, and the further you can project it forward the better. The downside to a pole this long is that it gets very heavy, even in carbon very quickly.

How much length matters versus centerline... It would probably take some serious modeling to tell you for sure.
__________________
Greg

- If animals weren't meant to be eaten then they wouldn't be made of food.
Stumble is offline   Reply With Quote
Old 27-05-2016, 03:26   #7
Registered User
 
UNCIVILIZED's Avatar

Join Date: Jun 2014
Location: Up the mast, looking for clean wind.
Boat: Currently Shopping, & Heavily in LUST!
Posts: 5,629
Re: Bowsprit length vs. exact centerline?

I'm assuming that you realize that the tip of the sprit can be on centerline, while the butt's far from it. Non?
And given such, is there so much hardware on your deck that you can't it mounts at an angle, with regards to the boat's CL. But with it's tip winding up dead center..
__________________

The Uncommon Thing, The Hard Thing, The Important Thing (in Life): Making Promises to Yourself, And Keeping Them.
UNCIVILIZED is offline   Reply With Quote
Old 27-05-2016, 04:04   #8
Registered User

Join Date: Feb 2011
Location: Eastern Mediterranean
Posts: 30
Re: Bowsprit length vs. exact centerline?

Uncivilized: The cleats that hold the aft end are in a predetermined position, as there are aluminum plates laminated in deck and those points. So they can't change. And the ring is done so the sprit doesn't collide with the roll bar of the anchor. Leaves only length to be varied.

I measured, it's 8 cm to starboard. I think I'll give it a try like that since nobody yelled 'you gonna break the rigg and sink the boat'. If it's no good, I can still make the sprit shorter.
__________________
Copprhead is offline   Reply With Quote
Old 27-05-2016, 05:37   #9
Registered User
 
TeddyDiver's Avatar

Join Date: Aug 2010
Location: Arctic Ocean
Boat: Under construction 35' ketch
Posts: 1,828
Images: 2
Re: Bowsprit length vs. exact centerline?

8cm is irrelevant for a cruiser IMHO. Aside, I'm considering having a horse in the end of the bowsprit for the jib to get it bit to leeward but not sure yet how the geometry works considering the stays..
__________________
TeddyDiver is online now   Reply With Quote
Old 27-05-2016, 07:14   #10
Senior Cruiser

Cruisers Forum Supporter

Join Date: Aug 2009
Location: between the devil and the deep blue sea
Boat: a sailing boat
Posts: 17,314
Re: Bowsprit length vs. exact centerline?

OK. 'as long as the sail is cut for this'. We are talking the same language.

Cheers,
b.
__________________
barnakiel is offline   Reply With Quote
Old 27-05-2016, 08:42   #11
Registered User

Join Date: Mar 2011
Location: fl- various marinas
Boat: morgan O/I 33' sloop
Posts: 1,102
Re: Bowsprit length vs. exact centerline?

Having suffered through several bridge construction jobs with metric plans (dumb DOT experiment) I had a few things drummed in my head-- 1/4 " = 6 mm, 1" = 2.54 cm. Your 8 cm issue is only about 3" and I doubt that anybody could detect that difference in tacking. Sailing is at best an approximating/ trial and error business so don't worry about it. In the unlikely even you decide it did matter you can always remove, cut down and replace the bow sprit.
__________________
Dave22q is offline   Reply With Quote
Old 27-05-2016, 10:05   #12
Registered User

Join Date: Sep 2010
Location: Boat in Turkey, Beach cat in Israel
Boat: Lagoon 400 & Nacra 6.0 beach cat
Posts: 630
Re: Bowsprit length vs. exact centerline?

Longer will be better as explained by Stumble.
And, the longer the bowsprit is, the angle between end of bowsprit and bow will be smaller.
On the other hand, the longer bowsprit will create larger moment upwards which should be countered by stronger bobstay better and lower anchored on the bow.
__________________
meirriba is offline   Reply With Quote
Old 27-05-2016, 11:20   #13
Registered User
 
hoppy's Avatar

Join Date: Sep 2009
Location: Melbourne, Australia
Boat: Jeanneau Sun Odyssey 40
Posts: 2,842
Re: Bowsprit length vs. exact centerline?

When I had the Selden bowsprit, I mounted the bow bracket first and then played around with positioning the end of the bow sprit to suit my sail (the J measurement I told the sailmaker). Whilst the bow bracket was fixed, I found there is enough play between the bracket and pole to give some angle of movement and to centre the tack point.

I had a lot more pole inboard than required, but as the end of it was in a position where I had access below deck, I mounted the pad eye and did not bother cutting the pole.
__________________
S/Y Jessabbé http://www.jessabbe.com/
hoppy is offline   Reply With Quote
Old 27-05-2016, 14:35   #14
Registered User

Join Date: Feb 2011
Location: Eastern Mediterranean
Posts: 30
Re: Bowsprit length vs. exact centerline?

Thank you all for your comments. The bow sprit is installed (8 cm version), now I just have to get the sail onto the furler and I'll be ready for a test drive. I'll report back here if there are problems.
__________________
Copprhead is offline   Reply With Quote
Old 27-05-2016, 18:20   #15
Marine Service Provider

Join Date: May 2012
Location: New Orleans
Boat: We have a problem... A serious addiction issue.
Posts: 3,940
Re: Bowsprit length vs. exact centerline?

Assuming a continuious furler just hook it up and launch out of the bag once. Then furl it to put it away. Trying to roll it up at the dock it.... Tricky.
__________________

__________________
Greg

- If animals weren't meant to be eaten then they wouldn't be made of food.
Stumble is offline   Reply With Quote
Reply

Tags
bowsprit

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
Jabsco Head O Ring Exact Size ? MarkJ Plumbing Systems and Fixtures 25 03-08-2017 11:42
How exact do electronics need 12 volts? MarkJ Marine Electronics 23 08-02-2014 21:21
Single Centerline Hawse Pipe.... SabreKai Anchoring & Mooring 1 06-12-2009 16:48
Cabin layout options - Pullman vs. Centerline Sterling General Sailing Forum 3 12-02-2009 10:06
Mounting fluxgate compass off Centerline?? alanperry Marine Electronics 22 13-07-2006 16:49



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 14:07.


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.