Davits

[Witzend]

CatSailor, for the most part I agree with you, which is why I'm posting my thoughts here.
Rich has pointed out something I had not even considered. Yes, there are many ways to get the motor up on the rail mount, but these day my back ain't one of them. I have even considered designing a telescopic pole that pull out from the end of the boom with a block.

 

[Witzend]

Rich, some simple trig will calculate the optimal distance the davit arms need to be placed apart. I will make the assumption that the heel angle will not normally exceed 15deg. I need to do some additional accurate measurements to get this right.

 

[Rich Stidger]

Questions,
1) Why didn't you just re-mount the arms closer together to solve the problem?
2) What do the vertical bars connect to that go up from your rails, and are they under tension or compression?
3) What do you do with your motor, assuming you have one?

1- I couldn't mount the arms closer because I have an opening hatch just inside each arm. See first picture below.

2- The vertical bars you see support the aft bow of my bimini. Compression probably.

3- I leave my motor on all the time. (see second picture below) Goes on in the Spring, off in the Fall. I haven't run into any weather that would require me to remove and stow the dinghy on the foredeck as I used to do before davits. I still keep the tie-down lines in place on the foredeck just in case.

 

[Rich Stidger]

Rich, some simple trig will calculate the optimal distance the davit arms need to be placed apart. I will make the assumption that the heel angle will not normally exceed 15deg. I need to do some additional accurate measurements to get this right.

Witzend-

You are correct, but in my case, and possibly in most cases, there is not a lot of choice of mounting location for the davit arms. Unless you have a long dinghy, like 10+ feet, or a very narrow stern like some of the 80's boats, most davits will need to be mounted approximately the same distance apart as the dinghy attachments.

Regarding the motor- maybe I missed your info, but do you have a really heavy motor? I have a 9'6" Achilles with a 3.5 hp Nissan. The motor weighs just 27#, maybe 30# with a full tank of gas. Certainly that can be a handful in choppy water or when handing over from boat to dinghy, but at 30# it is pretty manageable. Maybe you need to down-size from a big-block mill outboard to a string trimmer with a prop?

 

[Bill Roosa]

Requirements for davits?

Hey Witzend
I understand your trying to get the engineering right but why are you even considering davits? towing the dink is much easier when inland and when at sea you don't want to use davits anyway due to their not being very robust No matter how strong you make them a dink full of green water is going to get carried away.
Perhaps there are additional requirements that have not been stated. the reason I ask is I tried this on my 30' Catalina and while they were all fine a dandy they were in the long run just a PITA. Some stuff we found that discouraged us:
Short folks can't see behind when the dink is being carried without making an effort to see around the dink
You had to park the boat in the slip even further away to accommodate the dink sticking out (we doc stern to).
The aforementioned swinging problem.
The dink filling with water during a rain storm (mine had no drain and the cover was only about 90% effective.
The dink filling with snow in the winter or worse ice.
The stern nav light had to be relocated to make it visible with the dink being carried.
I, for one, was glad I made my davits and did not spend the money on them as we ended up taking them off after only one season.

 

[Snotter]

Hey Witzend
I understand your trying to get the engineering right but why are you even considering davits? towing the dink is much easier when inland and when at sea you don't want to use davits anyway due to their not being very robust No matter how strong you make them a dink full of green water is going to get carried away.
Perhaps there are additional requirements that have not been stated. the reason I ask is I tried this on my 30' Catalina and while they were all fine a dandy they were in the long run just a PITA. Some stuff we found that discouraged us:
Short folks can't see behind when the dink is being carried without making an effort to see around the dink
You had to park the boat in the slip even further away to accommodate the dink sticking out (we doc stern to).
The aforementioned swinging problem.
The dink filling with water during a rain storm (mine had no drain and the cover was only about 90% effective.
The dink filling with snow in the winter or worse ice.
The stern nav light had to be relocated to make it visible with the dink being carried.
I, for one, was glad I made my davits and did not spend the money on them as we ended up taking them off after only one season.

Furthermore...locking is harder dragging a dink; docking is harder alongside a pier when dragging a dink; and, it is a pain keeping a dink in the water in your slip next to your boat.

 

[Witzend]

Thanks Bill for your insights!
I wanted a 4 stroke (don't want the stink and mixing of the oil) that would plane, so I picked the 6 HP Tohatsu 55lbs, it will just barley plane with the two of us in a RIB, we tested a friends last summer.
I was in a very serious motorcycle accident many years ago and have potential back issues if I'm not careful (swim 6Km/week to maintain strength). Since I don't want to deal with removing the motor most of the time (bad idea to tow with motor attached when sailing in a good upper Chessy breeze,) thus it will be easier to use a good strong well designed davit system, and have the option to remove the motor if needed.
We are on a mooring, so rarely go into a slip.
It has a drain, I will have to be mindful of it.
It will be stored on my pier, lashed on it's side with a cover when at home port. I have already worked out the lifting system for my pier. We have been using my jet sky to get to and from the mother ship and left it on the mooring (always afraid someone would steal it, or run into it), when out cruising.
It will be stored inside during winter months.
Nav light, had not thought of that, thanks I will see what needs to be done to solve that problem if needed, thanks for pointing that out.

 

[Bill Roosa]

@Snotter

True, but that is what first mates and dingy racks are for.:dance:
But then I have an AWSOME first mate and the marina has a dingy cart and floating dock.
I mean seriously, walking forward with the painter is not what I'd call complicated.
Neither is making sure the dink is tied off short to the side of the boat away from the dock. couple of finders and an additional line to the dinks stern and you are done.
I do have to spend 10 minutes rowing (gasp, manual labor) all the way over to the dingy rack both before and after a trip however.

 

[Rich Stidger]

Short folks can't see behind when the dink is being carried without making an effort to see around the dink
You had to park the boat in the slip even further away to accommodate the dink sticking out (we doc stern to).
The aforementioned swinging problem.
The dink filling with water during a rain storm (mine had no drain and the cover was only about 90% effective.
The dink filling with snow in the winter or worse ice.
The stern nav light had to be relocated to make it visible with the dink being carried.

Bill makes some good points here. I had forgotten about relocating the stern light. That was a surprise when I discovered that it could not be seen. My solution (see pix below, before and after) was to move the light to my wind generator pole, but you could attach it to the bimini or radar pole as well.

As far as stern visability- Bill is absolutely correct. The view of the area directly behind you is not good and you really need to be aware and take precautions. This is particularly true when docking and un-docking as the stern can move toward the dock and pilings.

The davits also make using the stern scoop and ladder very difficult if not impossible for guests. So they may need to board at the side. Obviously when you are returning to your sailboat in your dinghy, there is no problem. In fact, the davits make a great hand-hold when moving from dinghy to sailboat.

However, the visibility forward is greatly improved now that the dinghy is not on the foredeck. And the lines that ties the dinghy down are not there and that eliminated a severe tripping hazard especially at night. And now the forward hatch can be opened without having to move the dinghy first.

Lastly, storing and launching the dinghy from davits is a one-person job. No longer does my wife and I need to remove the engine and stow, then pull the dinghy up over the lifelines and secure.

There is no free lunch. Everything has pros and cons. For us the pro's win.

 

[Witzend]

Upon further review the 310 stern light is mounted pretty low, so it my be OK from a distance. I will have to do some measuring and see. It will all depend on the final height. If not, since I don't have a wind gen pole or radar pole, I'm going to have to get creative here.
Yea, it's a give and take, and for our sailing MO I truly believe this will be a positive addition.

 

[BrianH]

You may want to consider how low that extra weight aft may push your stern. Even with my Hunter 44 I notice it sits lower in the water when i carry my dinghy.

 

[Witzend]

Drawing

I'm finally getting back to this and have a drawing that I will submit to Mark at Garhauer. I have calculated the optimum spacing between the two lifts to provide ~ 15deg. inward pull on the lift lines to add lateral stability and reduce possible line interference as suggested by Rich. I will make SS straps that will wrap around the tubing and create a tab for the connection points to mate to the standard Line Rail Fittings. Or I may just buy both parts.

 

[Buck420]

Witz,

My davits are pictured in the post: "Destinations/Name That Location".
Like Main's, they are OMS. I routinely leave the 15hp, 2 stroke Merk OB on the RIB, when they are up in the davits.

For what it's worth, I'd like to amplify one point made earlier. IMHO, the most important thing about any dingy/davit set-up is that, it (they) shouldn't move.... at all.
If the dingy swings, sways, or rocks even a little, ...and you find yourself if rough sea conditions, ... even that "minor" movement will be amplified catastrophically and you may well watch the whole thing be torn off the stern.
My dingy fits up snugly "into" the davits; pushes tightly against the two rear seats; is prevented from swinging and swaying by the inward angled (and cross braced) davit arms and is then strapped in, to further prevent it from moving. I further secrured the davit arms against being pulled down or thrust up ( as in being pooped) by adding addition support "tubes' ( the left one is barely visible in the picture at the edge of the left rear enclosure panel and under the fender).
With the dingy/davits thus secured so that the entire arrangement won't move, I do go offshore with the dingy in its davits ( at least coastal cruising up top 2-3 days with reasonable weather). I've had no problems cruising up and down the East coast over the past 10 years w/ this set-up.

 

[Witzend]

Thanks Buck, looks like a good arrangement you have.
The one issue I'm wrestling with is how far the davits should reach out.
1) If and make the reach half of the beam of the dink, which would put it right on the seat rails when lifted, but due to the slope of the transom the dink will scrape every time you raise and lower.
2) I could lever it out all the way so it has a clear shot up and down. I would then have to pull the dink into the rails for stability in transport, and would not be as stable.
3) I could compromise and have it closer, and only hit the bottom portion of the transom.
I'm tending to lean on option 3.

 

[Buck420]

Thanks Buck, looks like a good arrangement you have.
The one issue I'm wrestling with is how far the davits should reach out.
1) If and make the reach half of the beam of the dink, which would put it right on the seat rails when lifted, but due to the slope of the transom the dink will scrape every time you raise and lower.
2) I could lever it out all the way so it has a clear shot up and down. I would then have to pull the dink into the rails for stability in transport, and would not be as stable.
3) I could compromise and have it closer, and only hit the bottom portion of the transom.
I'm tending to lean on option 3.

My davits are set-up as per your "3".
As I lower the dingy, it hits the "scoop" transom about 1/2 way down and I have to "kick" it out a few times as it's going down.
Lifting, I have to use my legs to kick and push it away from the stern a few times as I raise it all the way up.
Not really much of a problem.
It woudl be impractical to have the dingy arms hold the dingy further out as this would ...
1- create an unacceptable moment arm, putting the dingy's weight even further aft.
2- prevent you from securely holding it against the stern rail to prevent movement.

 

[bljones]

You can spend time and money trying to make off-the-shelf items fit custom applications, or you can spend an exorbitant amount of money buying a custom made solution, or you can build your own:

 

[Witzend]

BLJones, you have any other pics? What did you make them out of?

 

[bljones]

Witz, the davit build is detailed here:

http://www.anything-sailing.com/showthread.php/5228-Low-Buck-Davits

 

[Witzend]

Well, that's quite a project, seems sound enough. I don't really have a feel for your lateral stability from you pictures, but I'm sure you have that worked out by now.
I think if I were going to make them from scratch I would buy 1.25 ss tubing wholesale and have a shop bend it. The end fittings are available as well to connect the lateral support and to attach to the existing railing. I have considered this approach but not much savings can be had.
How much $ do you have into it?
How much time did you spend?

 

[bljones]

Witz,

the davits are tied together laterally with two parallel cross bars, which also provide mounting points for a solar panel. the upright legs of the davits are secured to the pushpit rail with 12" lengths of 1" SS tube. You can sort of see the end result in the backgorund here:
http://s27.photobucket.com/albums/c.../?action=view&current=thanksgivingboat053.jpg

Total cost of materials was approx. $100. Total build time, about 20 hours.