Cruisers Forum
 


Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 28-03-2008, 08:07   #1
Sponsoring Vendor

Community Sponsor
Cruisers Forum Supporter

Join Date: Mar 2008
Location: Milton, Ontario
Boat: still dreaming...getting close...
Posts: 192
Bent Steel Davit Claims

Hey everyone, I was just looking through the April 2008 Cruising World and came across a claim that I think should be noted by some of the members on these boards. I won't get into any names or specifics but this could help someone avoid an unfortunate incident.

There is a set of bent, 304 stainless steel davits advertised that makes the claim of being able to safely handle 350 lbs. As a comparison, a quality davit manufacturer would only make stainless steel tubular davits that are rated up to 275 lbs. and that is with several features that are not included with this welded/bent system

A welded, bent steel davit will never be able to handle the forces that a 350 lb. tender will exert while operating. As I have mentioned in previous posts, when a steel tube is bent, the thickness is spread out at the bend, greatly reducing any strength. Simply put, a bent piece of steel will want to keep bending while under load.

The problem with welding components such as the compression strut, other than eventual unsightly corrosion at the weld, is that it only gives the illusion of strength. Instead of transferring the load downwards, as an independent strut would accomplish, a welded strut is acting only to hold the system together.

Another problem is that these types of systems are not adjustable to fit the needs of a sailor. Once the weld is made, that’s it, no more adjustments. A truly customizable system would have the ability to change heights and angles while maintaining superior strength.

These two photos show a welded, bent steel 350 lb. model davit and a 350lb. davit cast out of Almag-35. The cast model is also equipped with a 7:1 purchase while the bent davits only provide an insufficient 4:1. Take a look at each photo and let me know what you think. Those of you who are considering davits should take these points to heart, and those that already have a set of bent steel davits should consider making the switch.

Just a note, the extra hardware on the cast system on the right was added by the customer so that he could mount various items like a flag pole, etc.
__________________
Atkins & Hoyle Ltd. Over 40 years of Marine Innovation, Quality and Craftsmanship
Davits, Hatches, Ports, Hatch Repairs, Motor Lifts, Arches/Hardtops and Custom Designs www.AtkinsHoyle.com |atkinshoyle@dapa.com
Benjamaphone is offline   Reply With Quote
Old 28-03-2008, 13:18   #2
Registered User
 
DeepFrz's Avatar

Cruisers Forum Supporter

Join Date: Mar 2006
Location: Winnipeg
Boat: None at this time
Posts: 8,462
Are those aluminum castings and stainless tubes and bolts? If so I would love to see these units after they have been in salt water for a few years. Is that why I only saw boats from Toronto?
DeepFrz is offline   Reply With Quote
Old 28-03-2008, 13:24   #3
Registered User

Join Date: Mar 2006
Posts: 1,594
Where's my 'grain of salt"????
__________________
Randy

Cape Dory 25D Seraph
rtbates is offline   Reply With Quote
Old 28-03-2008, 13:30   #4
Registered User
 
Beausoleil's Avatar

Join Date: Jul 2007
Location: Solomons, MD USA
Boat: Formosa 51 Aft Cockpit Ketch - "Beausoleil"
Posts: 611
Images: 3
Unsolicited posting from a vendor? This belongs in the Vendor's forum.
Beausoleil is offline   Reply With Quote
Old 28-03-2008, 14:04   #5
Sponsoring Vendor

Community Sponsor
Cruisers Forum Supporter

Join Date: Mar 2008
Location: Milton, Ontario
Boat: still dreaming...getting close...
Posts: 192
Quote:
Originally Posted by DeepFrz View Post
Are those aluminum castings and stainless tubes and bolts? If so I would love to see these units after they have been in salt water for a few years. Is that why I only saw boats from Toronto?
Every touch point between any steel tube against aluminum has a delron sleeve to prevent the issues surrounding dissimilar metals which you alluded to. Any nut/bolt has a stainless helicoil with Teff-gel to prevent any corrosion there. The pictures are from Toronto because that is where I live and have my camera. However, there are many examples that show these products in salt water.
__________________
Atkins & Hoyle Ltd. Over 40 years of Marine Innovation, Quality and Craftsmanship
Davits, Hatches, Ports, Hatch Repairs, Motor Lifts, Arches/Hardtops and Custom Designs www.AtkinsHoyle.com |atkinshoyle@dapa.com
Benjamaphone is offline   Reply With Quote
Old 28-03-2008, 14:16   #6
Sponsoring Vendor

Community Sponsor
Cruisers Forum Supporter

Join Date: Mar 2008
Location: Milton, Ontario
Boat: still dreaming...getting close...
Posts: 192
Quote:
Originally Posted by Beausoleil View Post
Unsolicited posting from a vendor? This belongs in the Vendor's forum.
This has been discussed with the moderators. This post/thread is about how to avoid getting into a bad situation with bent steel davits. As far as I am concerned, there is no place for bent steel davits. This is what the post is in regards to.

As far as being an "unsolicited post"; I consider myself to be somewhat experienced in the area of davits. Yes, this is partly because I make them, and I am very proud of what we do. Therefore, when I see a bad situation I feel like it is a responsibility to make it known to others, solicited or not. I apologize if I have offended you by placing this post on a forum that you disprove of, but hope that you will continue to allow the moderators to police the boards.

Thank you, and if there are any other questions surrounding any of the points that I brought up in the post, I would like to have a chance to answer them.
__________________
Atkins & Hoyle Ltd. Over 40 years of Marine Innovation, Quality and Craftsmanship
Davits, Hatches, Ports, Hatch Repairs, Motor Lifts, Arches/Hardtops and Custom Designs www.AtkinsHoyle.com |atkinshoyle@dapa.com
Benjamaphone is offline   Reply With Quote
Old 29-03-2008, 08:00   #7
Registered User
 
scotte's Avatar

Join Date: Apr 2007
Location: SF Bay Area, CA, USA
Boat: Privilege 39
Posts: 664
Are you suggesting it's a problem with being bent, or being welded?
scotte is offline   Reply With Quote
Old 29-03-2008, 08:27   #8
Sponsoring Vendor

Community Sponsor
Cruisers Forum Supporter

Join Date: Mar 2008
Location: Milton, Ontario
Boat: still dreaming...getting close...
Posts: 192
Quote:
Originally Posted by scotte View Post
Are you suggesting it's a problem with being bent, or being welded?
Both, because most bent steel davits are held together with welds. Bending is a very inefficient way to join tubes and make angles with them. Instead of keeping the integrity of the metal, a bend spreads out the wall thickness of the tube at each and every bend. It's important to note that these are also the areas under the highest load.

Welds are used in these bent systems because they have not been designed with an innovative way to join different sections. The least creative solution is to make a weld. Welds are also points where corrosion will attack because the welding material and methods are often below true marine-grade standards. Welds are also inherently weaker than a casting joint.
__________________
Atkins & Hoyle Ltd. Over 40 years of Marine Innovation, Quality and Craftsmanship
Davits, Hatches, Ports, Hatch Repairs, Motor Lifts, Arches/Hardtops and Custom Designs www.AtkinsHoyle.com |atkinshoyle@dapa.com
Benjamaphone is offline   Reply With Quote
Old 29-03-2008, 13:53   #9
Senior Cruiser
 
Alan Wheeler's Avatar

Cruisers Forum Supporter

Join Date: Dec 2003
Location: Marlborough Sounds. New Zealand
Boat: Hartley Tahitian 45ft. Leisure Lady
Posts: 8,038
Images: 102
In your opinion Ben. Personaly I really don't agree with your comments. I happen to have custom made SST Davits that have wleds and bends and it is strong, never had a problem and I stand by it's strength. Sure you could argue a point that a cast is stronger. But if the Davit is a good design, has been made well from the begining, then it will have no problems. I suspend a 3.5m inflatable with solid ply floor, inflatable Keel, with a 15Hp outboard and full fuel tank and anchor from my Davits. And I have also stood inside the inflatable while suspended. No problems. The greatest weight it had to enjure was when the drain hole got blocked ant the inflatable filled with water. I don't know what the thing must have weighed, but we would talking tons. In the end, the attachment points on inflatable gave way, not the Davits. Of and I also have the Mizzen sheet travelr mounted to the top of the Davits. So they take a lot or sideways and lifting force as well.
__________________
Wheels

For God so loved the world..........He didn't send a committee.
Alan Wheeler is offline   Reply With Quote
Old 29-03-2008, 15:07   #10
Sponsoring Vendor

Community Sponsor
Cruisers Forum Supporter

Join Date: Mar 2008
Location: Milton, Ontario
Boat: still dreaming...getting close...
Posts: 192
Quote:
Originally Posted by Alan Wheeler View Post
Sure you could argue a point that a cast is stronger.
This is basically my point. I agree that a system could be welded and bent together but that it would require thicker walled and higher OD stainless steel, increasing the weight dramatically. The original post was about a bent system that is rated at 350 lbs. and the weight of your tender + gear, etc. is no more that 250-275 lbs. (in my opinion, I could be wrong and would definitely confirm before suggesting any equipment choices.)

Usually bent steel davits don't have many problems while you’re tied up at the dock. It’s when you’re at sea and the tender is being slammed up and down. Even in moderate, Sunday afternoon conditions, the extra load experienced on the davits by the tender while underway is considerable. I have seen many, many bent steel configurations buckle under these loads.

I don't think that there is any question about how a stainless steel tube weakens as it is bent. When the steel is originally produced, the 'grain' sets up in a certain direction, contributing to much of the final strength. By bending the tube, you break that configuration and make the metal pliable again.

Have you experienced any corrosion at the welds? In my experience this often the first place that you will see salt water reacting with your hardware.

These are my opinions and I stand behind them. However, I appreciate any debate and dialogue as I see it as a chance to add to my experience.
__________________
Atkins & Hoyle Ltd. Over 40 years of Marine Innovation, Quality and Craftsmanship
Davits, Hatches, Ports, Hatch Repairs, Motor Lifts, Arches/Hardtops and Custom Designs www.AtkinsHoyle.com |atkinshoyle@dapa.com
Benjamaphone is offline   Reply With Quote
Old 29-03-2008, 15:22   #11
Long Range Cruiser
 
MarkJ's Avatar

Join Date: Dec 2007
Location: Australian living on "Sea Life" currently in England.
Boat: Beneteau 393 "Sea Life"
Posts: 12,822
Images: 25
Quote:
Originally Posted by Benjamaphone View Post
... As far as I am concerned, there is no place for bent steel davits. ....";......

because I make them, ....
Nicolle and I have been a bit surprised about some of the cultural differences in the US from home in Aus. We are stuck, waiting for our boat to be ready and the TV has been on a bit. Cable from the US.

Its surprising how many TV advertisers slag off the opposition including quoting of names.

I am sure that I don't like it! Call me weird, but I don't mind people telling me how their product is good and what their Unique Competitive Advantage is, but I don't like belittling of the opposition. I’m not a mod here so policy is nothing to do with me, and I’m not trying to tell the mods my thoughts. I’m just telling Ben my thoughts. There is a spot on this forum you can tell us all about your product (even give us a special offer to save us some cash!) but please I'm only interested in what you tell us about your product, not what you feel about someone else’s.

Mark
__________________
Notes on a Circumnavigation.
OurLifeAtSea.com

Somalia Pirates and our Convoy
MarkJ is offline   Reply With Quote
Old 29-03-2008, 15:31   #12
Sponsoring Vendor

Community Sponsor
Cruisers Forum Supporter

Join Date: Mar 2008
Location: Milton, Ontario
Boat: still dreaming...getting close...
Posts: 192
These opinions come from experience that I have accumulated by building my own bent system. A decade ago, we experimented with a bent steel model, called the Euro-Lift and ultimately had it scrapped for many of the reasons that I have described. I would not offer an opinion that I developed by conjecture, bias or heresy and generally will try anything to solve a problem. My conclusions come from a trial and error approach and this has served to create some great solutions.
__________________
Atkins & Hoyle Ltd. Over 40 years of Marine Innovation, Quality and Craftsmanship
Davits, Hatches, Ports, Hatch Repairs, Motor Lifts, Arches/Hardtops and Custom Designs www.AtkinsHoyle.com |atkinshoyle@dapa.com
Benjamaphone is offline   Reply With Quote
Old 29-03-2008, 15:47   #13
Long Range Cruiser
 
MarkJ's Avatar

Join Date: Dec 2007
Location: Australian living on "Sea Life" currently in England.
Boat: Beneteau 393 "Sea Life"
Posts: 12,822
Images: 25
Quote:
Originally Posted by Benjamaphone View Post
These opinions ....
Thats the point, yours are only opinions.

Our Advertising Standards say your opinions must be more carefully couched in advertising:

Quote:

1.3
Advertisements shall not contain a misrepresentation,
which is likely to cause damage to the business or goodwill

of a competitor.
http://www.adstandards.com.au/pages/...hics_final.pdf

The point is no court or legislation has made your competitors products illegal. They can claim you misrepresent the facts. As the advertising medium (CF etc) cant investigate all statements then they can not determain misrepresentation.

So what you are saying may well be ok for some cultures used to slagging off the competitors. But the tactic wont work with all. We are not used to it.

__________________
Notes on a Circumnavigation.
OurLifeAtSea.com

Somalia Pirates and our Convoy
MarkJ is offline   Reply With Quote
Old 29-03-2008, 16:03   #14
CF Adviser
 
Pelagic's Avatar

Join Date: Oct 2007
Boat: Van Helleman Schooner 65ft StarGazer
Posts: 10,280
I am just going through this same dilemma with a welder who strongly advises against bends on stainless pipe for a heavy load bearing weight that is subject to momentum in a seaway.

Obviously any system is only as strong as its weakest point, which you have correctly pointed out are the bends.

Ben, the silent majority thanks you for your caution!
Pelagic is offline   Reply With Quote
Old 29-03-2008, 16:38   #15
Sponsoring Vendor

Community Sponsor
Cruisers Forum Supporter

Join Date: Mar 2008
Location: Milton, Ontario
Boat: still dreaming...getting close...
Posts: 192
Thank you, Pelagic. Safety first is what I say.

MarkJ, this is not an advertisement, it is merely a commentary on a technique that is used throughout the industry. I 'slag' no one and only want to highlight some of the issues surrounding the subject. As far as my opinions go, I have no reservations about expressing them and the only rules surrounding this is that they must be separated from my professional opinions.

I come from a culture that uses the scientific exchange of ideas to come up with better solutions. This means the careful examination of every method and material and then making choices based how they perform. I submit to you that this is an exercise in solving problems, not engaging in slander.
__________________
Atkins & Hoyle Ltd. Over 40 years of Marine Innovation, Quality and Craftsmanship
Davits, Hatches, Ports, Hatch Repairs, Motor Lifts, Arches/Hardtops and Custom Designs www.AtkinsHoyle.com |atkinshoyle@dapa.com
Benjamaphone is offline   Reply With Quote
Reply

Tags
davits

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
Davit pulley turkish6 Auxiliary Equipment & Dinghy 14 28-03-2008 07:25
Davit connection points on tender aquaman_001 Auxiliary Equipment & Dinghy 8 21-02-2008 07:33
Bent Boom clausont Deck hardware: Rigging, Sails & Hoisting 10 29-11-2007 18:34
Philosophical bent... bcguy General Sailing Forum 10 30-12-2006 10:16
Does anybody have experience with this Davit system??? exposure General Sailing Forum 5 27-08-2004 07:57

Advertise Here


All times are GMT -7. The time now is 04:23.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.