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Old 31-12-2018, 12:43   #1
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Windage implications of dinghys, davits, and arches

I see so many larger cruising boats that are set up with arches and davits, sometimes a dinghy in the davits, and it seems to me that there must be so much windage that the upwind ability of the boat is severely compromised.


Is this as serious a problem as it appears to be?

Are these conscious tradeoffs or unknowing ones?



Is there any sort of counterculture that isn't buying into the "15 hp aluminum RIB" part of the lifestyle?


Given the importance of having a dinghy, what are the best choices for minimizing windage?
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Old 31-12-2018, 12:48   #2
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Re: Windage implications of dinghys, davits, and arches

It doesn't make any different on sailing ability when mounted on stern davits, but it sure makes launching the dinghy much easier. Not much time is spent sailing to windward anyway, convenience of use far outweighs the small amount of time spent sailing.
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Old 31-12-2018, 12:51   #3
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Re: Windage implications of dinghys, davits, and arches

Obviously, this is a matter of degree. We've all seen a few absurd arches.



On many boats the davits are largely within the wind shadow of the Bimini or hard top when the AP is 20some degrees. On my last boat (cruising cat) the dingy was barely visible from the AP angle and there was very little wind near the dingy. It was in the shadow of the hard top. No arch, and the dingy was lower than most monohulls could tolerate (the dingy fits between the hulls). In fact, just look at he header on this forum page.
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Old 31-12-2018, 12:54   #4
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Re: Windage implications of dinghys, davits, and arches

Are you referring to windage under way, at anchor, on a mooring, or in general? IMHO, having your tender on davits is the best alternative. I don't notice any effect on windage under way; and at anchor or mooring, security concerns frankly overrule any slight increase that a davited dink might add to my already obscene swing room in a cat. (Confessions of a lifelong monohull sailor).
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Old 31-12-2018, 13:07   #5
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Re: Windage implications of dinghys, davits, and arches

Jammer,

I agree with your thoughts that dinghies on davits while sailing is just a BAD idea, for lots of reasons. So much so that when we installed our arch to hold our solar panels we skipped the nominal additional cost of the davits. The only reason to have a dinghy on davits is for connivance--there is nothing that is better about it. It worse for windage. It is WAY worse for weight distribution, it is less safe for the dinghy. Other than being easy, I can't think of a good reason to do it.

One of our objectives has always been "clean decks." One is just plain esthetics. We do not want to be the boat that pulls into the anchorage, and the first thought anyone has is "liveaboard cruiser" because of all the crap on deck. But I have also been in weather bad enough that tons of green water swept across the decks for days. It is not where my dinghy, or anything else, should be. I have had stanchions ripped out by the force of water hitting a fairly small solar panel. I can only imagine what happens with the kayaks and SUPs that people seem to hang on their rails these days.

To square the circle of having a dinghy with reasonable performance, but still could be put away safely we chose a 10.5 foot folding RIB. It has been our "get around" for three years of full time cruising, and if it exploded tomorrow, I'd go the same way again in a heart beat.

It folds into a package that is small enough that it can drop into our stern locker, for passages, or be tied down on the aft deck for day sails. It is out of the way both physically and visually. We have an electric inflator that makes it fast and easy enough to inflate that we don't hesitate to let the air out and fold it up when ever we move the boat.

If we need to hoist it out of the water while at anchor, we use a three point harness and a halyard, and bring it to the rail. Just as quick, easy and secure as davits.

So... while we might have signed on to the 15HP RIB lifestyle... we found a way to do it without compromise to our yacht's sailing ability and good looks.
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Old 01-01-2019, 11:08   #6
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Re: Windage implications of dinghys, davits, and arches

Hi Billknny,
What model folding RIB do you have?
Also my concerns with having all that gear aft is it causes the boat to broach downwind in heavy weather, I have to much up there myself which is bit of a worry.
Cheers
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Old 01-01-2019, 11:48   #7
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Re: Windage implications of dinghys, davits, and arches

The RIB with 15horses behind it are everywhere. I chose not to.
The RIB has three main strikes against it:
1. Ugly.
2. Can only be motored. Rowing or sailing performance is horrible.
3. Short life. Sure, there are things one can do to extend it's life, but don't expect it to last very long.
And did I mention ugly?

I have a skin on frame dinghy with classic lines from gaboats.com. She weighs about 35 lbs and is often the prettiest boat in the marina. She rows so nicely I've not yet felt the need to hang a motor on her transom. She's so light I can pick her up and place her on deck when needed, or towing she generates negligible drag.

I don't have an arch, but my bimini probably creates windage.
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Old 01-01-2019, 11:52   #8
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Re: Windage implications of dinghys, davits, and arches

Quote:
Originally Posted by Jammer View Post
Is there any sort of counterculture that isn't buying into the "15 hp aluminum RIB" part of the lifestyle?
I suppose if you have a large yacht then that is an option, but there is no way we could or want to have a rib and 15hp engine. Instead we manage quite happily with a small 2.7m tender and small outboard. The latest one is an old 8ft Avon with a honda 2.3hp. We stored the previous dinghy sideways on the stern and engine on the pushpit, but that is quite a bit of weight on the stern. Dinghy now deflated and stored just in front of the mast when at sea. The honda is great and I can easily climb up the stern with the engine in one hand. I can't think of an anchorage or estuary that we have visited over the last 10 years that needed anything larger in England or France.


I see YT videos of people standing up in dinghies and planning through Caribbean anchorages at ridiculous speeds, why? and what about swimmers and other water users.
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Old 01-01-2019, 11:57   #9
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Re: Windage implications of dinghys, davits, and arches

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Originally Posted by Jammer View Post
I see so many larger cruising boats that are set up with arches and davits, sometimes a dinghy in the davits, and it seems to me that there must be so much windage that the upwind ability of the boat is severely compromised.

Is this as serious a problem as it appears to be?

Are these conscious tradeoffs or unknowing ones?

Is there any sort of counterculture that isn't buying into the "15 hp aluminum RIB" part of the lifestyle?


Given the importance of having a dinghy, what are the best choices for minimizing windage?
The bottom line is that davits are for convenience and dinghy security and, like all things boat, it is a tradeoff.

That said, I don't think such a configuration is necessarily a bad choice on coastal cruising in rather sheltered waters where you are anchoring out every night or in ports with a history of theft.

The problem with davits is their use offshore and on passagemaking when the weather turns to its worst. Most professional articles I have read are clearly against their use in those environments. The additional stern weight is undeniable. It also makes the installation of a wind vane more complex/difficult/expensive and I consider that piece of equipment necessary for offshore passages. When I installed an arch for solar panels on my boat, which has a wind vane, I specifically did not include a davits for those reasons.

For offshore travels the dinghy should either be deflated and stored or safely secured on the bow of the boat.

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Old 01-01-2019, 13:54   #10
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Re: Windage implications of dinghys, davits, and arches

In my homeport a visiting yacht tied up to the public wharf for water. The owner wandered off to the shops and when he returned his new inflatable and outboard was missing from the davits!
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Old 01-01-2019, 14:08   #11
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Re: Windage implications of dinghys, davits, and arches

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Originally Posted by Qayaq View Post
Hi Billknny,
What model folding RIB do you have?
Also my concerns with having all that gear aft is it causes the boat to broach downwind in heavy weather, I have to much up there myself which is bit of a worry.
Cheers
Qayaq,

We have a folding RIB that was marketed by West Marine. It was made to the same design as the boats sold by F-Rib, and at the time was the only folding RIB available in the USA market. Now that F-RIB has entered the US market in a significant way, West Marine no longer sells that product, I have no idea if there were patent conflicts, or it was licensed or what...

I was with a friend at an F-RIB dealer just the other day as he was buying one in preparation for longterm cruising. It is a nice piece of kit.

Any time you add weight up high, and out at the ends of a boat, it is a bad thing for handling and performance. A typical small RIB with its engine mounted scales in at close to or over 200 lbs (100 kg).

The idea that performance will not suffer when hanging so much weight 6 to 10 feet above the center of buoyancy, and out behind the hull just shows ignorance of the most basic of sailing physics.
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Old 01-01-2019, 15:06   #12
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Re: Windage implications of dinghys, davits, and arches

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Originally Posted by Kenomac View Post
It doesn't make any different on sailing ability when mounted on stern davits, but it sure makes launching the dinghy much easier. Not much time is spent sailing to windward anyway, convenience of use far outweighs the small amount of time spent sailing.
It sure as hell does slow the boat when sailing to weather.
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Old 01-01-2019, 15:08   #13
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Re: Windage implications of dinghys, davits, and arches

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Qayaq,

We have a folding RIB that was marketed by West Marine. It was made to the same design as the boats sold by F-Rib, and at the time was the only folding RIB available in the USA market. Now that F-RIB has entered the US market in a significant way, West Marine no longer sells that product, I have no idea if there were patent conflicts, or it was licensed or what...

I was with a friend at an F-RIB dealer just the other day as he was buying one in preparation for longterm cruising. It is a nice piece of kit.

Any time you add weight up high, and out at the ends of a boat, it is a bad thing for handling and performance. A typical small RIB with its engine mounted scales in at close to or over 200 lbs (100 kg).

The idea that performance will not suffer when hanging so much weight 6 to 10 feet above the center of buoyancy, and out behind the hull just shows ignorance of the most basic of sailing physics.
What he said.
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Old 01-01-2019, 15:17   #14
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Re: Windage implications of dinghys, davits, and arches

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That said, I don't think such a configuration is necessarily a bad choice on coastal cruising in rather sheltered waters where you are anchoring out every night or in ports with a history of theft.
I guess a lot depends on your definition of "coastal" and "sheltered". I saw a 38 foot boat come into Newport, RI after a passage from Block Island. Certainly what most people would call "coastal cruising", although maybe not not entirely "sheltered".

They had a dinghy on davits, and in that relatively short passage they were pooped. The entire arch and davit system was totally pretzeled and the dinghy was destroyed.

It is always better to learn a lesson from somebody else's painful mistake.
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Old 01-01-2019, 15:34   #15
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Re: Windage implications of dinghys, davits, and arches

Yep, us cruisers do connive on a lot of stuff.

On my previous boat I stored the dingy on the for deck whilst under open sea passages and had a sort of crane system to do the transfer. Whilst it was convenient enough to do occasionally it was not so convenient to do every night whilst at anchor and I suffered the mischief that dingys get up to when unobserved.

On this boat I installed a davit and now lift the dingy out of the water when it's not in use, much more convenient - no mischief or barnacles, harder for thieves to steal - the positives far outweigh the negatives.

I abhor going to windward and if required to by circumstances usually motor and consequently a bit more windage is a small price to pay for the convenience of davits.
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