Air Draft vs. Bridge Height vs. Heel - 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 > General Interest Forums > Seamanship & Navigation
 Not a Member? 

Seamanship & Navigation Forum devoted to seamanship and navigation topics, including paper and electronic charting tools.


Like Tree1Likes
Reply
 
LinkBack Thread Tools
  #1  
Old 02-07-2012
CarbonSink62's Avatar
Load Bearing Member
 
Join Date: Sep 2011
Location: Derry, NH
Posts: 467
Thanks: 7
Thanked 4 Times in 4 Posts
Rep Power: 3
CarbonSink62 is on a distinguished road
Air Draft vs. Bridge Height vs. Heel

Come laugh at the newbie!!

There is a drawbridge between my new mooring and the big blue sea with a closed height of 19'; my little 18' boat has an airdraft of 23' 2", I'm calling it 25' with the 'vane and a safety margin.

My trig was all rusty but I found an online calculator that showed if I induce a heel of 40 degrees I should be able to slip under the bridge without having to wait for it to be raised.

I don't need my math checked (but you're welcome if you want) I just want to know if this is a done thing. With a displacement of only 1500# it seems like it wouldn't be too tough to get it to heel over. I'd practice in open water to see how handling is affected and I'd need crew to do the heeling while I drive. If I heel over to starboard that would keep the engine in the water.

I don't see much risk unless it was really crowded; since the bridge only opens on the half hour it seems like I could save some time.

Do people do this?

Is there some cool name for it? Sailing has the best terminology of any sport.

The bridge is being replaced soon with one that will have a height of 21' that makes it even more tempting.
__________________
Zen Again

Catalina 25 #2818

Testing a mother's love since 1962
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Reply With Quote Share with Facebook
  #2  
Old 02-07-2012
Faster's Avatar
Just another Moderator
 
Join Date: Sep 2005
Location: New Westminster, BC
Posts: 14,390
Thanks: 63
Thanked 160 Times in 157 Posts
Rep Power: 10
Faster has a spectacular aura about Faster has a spectacular aura about Faster has a spectacular aura about
40 degrees is a long way over.. even on a small boat maintaining that angle may be difficult and if something goes wrong while you're under the bridge...

There is a video out there of a rather large boat using ballast bags hung from the rig, so it has been done.
killarney_sailor likes this.
__________________
Ron

1984 Fast/Nicholson 345 "FastForward"

".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
Reply With Quote Share with Facebook
  #3  
Old 02-07-2012
denverd0n's Avatar
Senior Member
 
Join Date: Jun 2008
Location: Tampa, FL
Posts: 776
Thanks: 0
Thanked 14 Times in 14 Posts
Rep Power: 6
denverd0n is on a distinguished road
40 degrees is way, WAAAAY over! What most people consider an extreme angle of heel when they are sailing is probably no more than half that. I think I would just wait for the bridge to open.
Reply With Quote Share with Facebook
  #4  
Old 02-07-2012
JordanH's Avatar
Senior Member
 
Join Date: Dec 2008
Location: Canada
Posts: 324
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 6
JordanH is on a distinguished road
Will you still have proper steerage and propulsion at 40 degrees of heel?

The mentioned video is this one: Boat Balls - YouTube

How will you attach the water bags to your masthead? If the sheaves are fixed, will the halyard jump out of the track and jam? How long will it take to rig, and will the time (and risk) savings be worth it?

Have you had the boat over that far before? I know our Contessa likes 15-25 degrees of heel, but our narrow hull likes it over that far before it locks in. I wouldn't feel comfortable at 40 degrees... and inanimate objects in the cabin and the animate objects in the cockpit wouldn't like 40 degrees either.
Reply With Quote Share with Facebook
  #5  
Old 02-07-2012
sailortjk1's Avatar
Senior Member
 
Join Date: Dec 2005
Location: Porter, IN
Posts: 4,647
Thanks: 1
Thanked 1 Time in 1 Post
Rep Power: 10
sailortjk1 has a spectacular aura about sailortjk1 has a spectacular aura about
Every half hour is very fortunate if you ask me. How much time are you going to save?
Not worth the risk in my opinion.

Does the mast step have a tabernacle? See where I am going with this? If you’re in such a rush to get out, it might ne easier to drop the stick on an 18’ boat and re-step it on the other side of the bridge.
__________________
Courtney is My Hero

If a man is to be obsessed by something, I suppose a boat is as good as anything, perhaps a bit better than most - E.B. White
Reply With Quote Share with Facebook
  #6  
Old 02-07-2012
CarbonSink62's Avatar
Load Bearing Member
 
Join Date: Sep 2011
Location: Derry, NH
Posts: 467
Thanks: 7
Thanked 4 Times in 4 Posts
Rep Power: 3
CarbonSink62 is on a distinguished road
I guess 40 deg is pretty far.

I'd feel pretty stoopid if I got stuck under there!

A more moderate heel of 20 deg only shaves 1.5' off the air draft.

So, it's good to know what it would take but not worth the risk for such a small gain.

Thanks for talking me down off the roof.
__________________
Zen Again

Catalina 25 #2818

Testing a mother's love since 1962
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Reply With Quote Share with Facebook
  #7  
Old 02-07-2012
AdamLein's Avatar
Senior Member
 
Join Date: Nov 2007
Location: Coquitlam, BC
Posts: 1,866
Thanks: 1
Thanked 0 Times in 0 Posts
Rep Power: 7
AdamLein will become famous soon enough
Quote:
Originally Posted by CarbonSink62 View Post
the bridge only opens on the half hour it seems like I could save some time.
Lucky you. My bridge is plenty high but I can only buck the tide twice a day.
__________________
s/v Essorant
1972 Catalina 27
Reply With Quote Share with Facebook
  #8  
Old 02-07-2012
hellosailor's Avatar
Senior Member
 
Join Date: Apr 2006
Posts: 10,040
Thanks: 0
Thanked 50 Times in 49 Posts
Rep Power: 10
hellosailor has a spectacular aura about hellosailor has a spectacular aura about
Forty degrees is awfully close to halfway broached. If you're going to do that on a regular basis, put the video on utube, sell advertising space and tickets for the live performance, because folks don't get to see that very often.

You probably CAN do it, but wouldn't it be more fun to dynamite the bridge?
(Now kids, don't do that at home, dynamite is strictly for professional use under adult supervision!)
Reply With Quote Share with Facebook
  #9  
Old 02-07-2012
Senior Member
 
Join Date: Sep 2006
Posts: 2,179
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 8
Rockter will become famous soon enough
Your trigonemetry is correct.

The heel angle needed for the 19 ft bridge clearance is given by...

a = invcos{19/25} = 40.53 deg

...and for the 21 ft bridge clearance...

b = invcos{21/25} = 32.86 deg.

Those are first estimates, as the mast will not pivot perfectly around a single point as the boat heels.

Those are quite aggressive heel angles.

It's a risky business though. If you get it wrong, you will smash the masthead and fittings on the bridge. You may even bring the mast down.
.
Reply With Quote Share with Facebook
  #10  
Old 02-07-2012
Senior Member
 
Join Date: Jun 2004
Location: western LI sound, L.I., N.Y.
Posts: 411
Thanks: 1
Thanked 4 Times in 4 Posts
Rep Power: 10
HUGOSALT is on a distinguished road
Heeling to that degree is not a viable option on an ongoing basis.
You mention the big blue sea, might you have a tide, that could range up to 8'+ in your neck of woods. Bridge clearance is published
based on mean high water...so if assumptions above are close you
may have about half time that you clear...??
If close remove vane, but I would bribe a buddy with a dinghy/powerboat and check out first with a few 10' lenghts of pvc.
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
Double Checking My Math - Bridge Height DrB General Discussion (sailing related) 8 10-13-2011 05:42 PM
A puzzle -- how to heel to pass under a bridge PopeyeRideau General Discussion (sailing related) 5 07-14-2011 01:40 PM
Understanding NOAA bridge vertical height alanr77 General Discussion (sailing related) 8 06-29-2010 08:30 PM
Mast height/Draft - What limitations will I have? labatt Cruising & Liveaboard Forum 49 10-15-2007 12:58 PM


All times are GMT -4. The time now is 05:31 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