Dock-based davits boat lift....

[mlmarvin]

My first post here...thanks in advance for any help. I live on the Chesapeake Bay, just built a dock, but have low water levels, so every inch matters as we look to buy a boat that will work "most" of the time (16-17' Whaler or Edgewater, probably). I thought a davits boat lift would be the best since nothing goes under the boat, so I can maximize the water I do have w/o having to account for the lift structure itself.

Anyone used a piling-based davits boat lift before? Problems I haven't thought about? Too much stress on the davits hooks on the boat (L-316 construction on both boats we're looking at)? Should I consider a sling? Problems because of high winds? Alternatives? HELP!!!

 

[William_H]

Not really what you are talking about but a guy around here is selling (not successfully) a submersible boat lift. The tanks are filled with water the boat (Mobo) is driven on then the tanks are pumped (blown) out to raise the hull out of the water. The reason here not being tide so much as prodigious weed growth. The idea may give you some food for thought.
I would imagine your davits would be stronger and simpler if supported from both sides ie 4 piles with cross members which you attach 2 winches to lift the boat. Most boats made for lifting are lifted by keel bolts.
olewill

 

[Blueboatman]

Have you considered building a ramp/roller/electric winch typed set up? I ask only because you say that you have built a dock and the technology and parts are similar and readily available.
Floridas shallow (and storm prone) waterways have many devices for 'dry sailing'your boat as observed at the end of many docks on the ICW,you may have to research via contractors there for specific ideas?

 

[sarabande]

HI, and welcome to the Forum.

One of the design issues with davits is to ensure that the effective point of attachment is ABOVE the centre of gravity of the boat to be lifted. I remember only too well screwing a couple of eye bolts into the keelson of a 11 ft dinghy, and hoisting away, only to find that the tender tipped sideways dramatically.

Might be worth looking at this site for a few ideas and advice.
www.davitmaster.com/

 

[mlmarvin]

very good reminder, thanks! I've narrowed the purchase decision to either an Edgewater 170 or a BW Montauk 170 (hey, i'd take advice on THAT, too!)...both of them have L-316 davits hardware available or installable by the manufacturer.

 

[mlmarvin]

Thanks, but that approach requires more water than I have much of the time...just returned from a test drive of the Montauk and it did an excellent job in low water, including when we touched a few times (very sandy). nice boat.

 

[DaveS]

This is drifting a bit from the original question, but...

I hoist my dinghy to the boat using transom mounted davits. The dinghy is a "doughnut", i.e. round stern, no transom, type. My attachment points consist of spliced slings made up of 5 mm laid line which terminate in carabiners and which in effect lift the dinghy by its floorboards. This is perfectly stable in lifting as the caribiners, which snap on to the fall blocks, are well above the dinghy's CofG. OTOH if the dinghy is then tilted(e.g. to empty out water) the effective pivot point is the sling splices which are close to the CofG so the dinghy is almost equally stable in a horizontal or vertical position! I've always thought of this as an interesting little paradox...

 

[geoffatstanpit]

I think it might be helpful to explain that a dock is a different thing in the UK and the US. If the reply comes from the UK then the writer will assume that your dock is "an area within a harbo(u)r enclosed by piers or wharves". If memory serves a US dock is what would be called in the UK a "jetty" i.e. a structure built out from the shore to help access to boats or even a marina berth.

 

[mlmarvin]

Re: Dock-based davits lift....and Whaler versus Edgewater question...

I have considered that, but am unable to expand the dock any further, so nothing that can float, and the idea of a full winch system would be cumbersome, as the dock platform is about 3 to 4 feet above the water line, so the angle of ascent would be so steep when winching up that I would risk damage to the prop/engine each time. thanks for the thoughts, everyone.

Now, about that Edggewater versus Montauk question....

 

[mlmarvin]

Apologies for the unintended confusion...and thanks for the new info! This is a dock in Annapolis, Maryland, 8 feet wide and extending 75 feet into the water about 3 feet above the high tide line, supported by pilings.

 

[mlmarvin]

Interestingly, I asked the owner of the Boston Whaler dealership about this, and he said the only time he'd seen severe structural damage caused to a Whaler by a lift was through slings under of a Whaler on a davits lift, because the effect was akin to a "folding" of the foam, which caused a massive structural failure. Don't know if that's a Whaler-specific issue or ??

 

[sarabande]

Sounds as if there might be some friction from the "slings" which is preventing the dinghy overbalancing. Difficult to say wht's happening without a picture, but the laws of physics still hold good even in the metaphysical universe of The Lounge.