Raised cabin vs flush deck

[gmat]

When you say extra windage, are we talking 10% or 50%. I am trying to understand the effect on boat speed of the extra windage.

 

[tom28571]

When you say extra windage, are we talking 10% or 50%. I am trying to understand the effect on boat speed of the extra windage.

Probably well under than your 10% in all cases but it is too dependent on a particular design to say. I see the one design San Juan 21s where some are flush deck and some are trunk cabin boats racing against each other regularly with no rating penalty. There is bound to be some extra windage but it is apparently not enough to cause concern.

 

[PAR]

I use to race with San Juans and the only time windage was really noticeable among the two types was in very light winds, naturally up wind was the place the extra windage hurt.

 

[dlblandjr]

Many thanks for the interesting thoughts posed herein, I am an old codger m'self, I had a old steel hull ketch of 43' unknown designer, built in kiwi 1940's I loved the look of that ship. However now that would be too much work for me to sail myself, so I've a little 26' sloop, which just happens to have a similar superstructure, if it could be called such, as the 20' er pictured above,. When I got it, I thought it rather queer looking, however, I have come to really enjoy the tuff little girl greatly! I would point out I was amazed at her wave taking ability, tremendous stability in the little girl! Sailing her on Lake Superior now, Good day all!

 

[capt vimes]

wehn we are talking racing - in my eye the only situation were windage is of any concern - the flush decks have another big advantage:
sheeting angle...
see the images below - do you think those tight sheeting angles would be possible on a stepped deck?

 

[Skyak]

A lot of monohulls have side decks for accessing the front of the boat, and a raised cabin in the center of the boat giving head room below.

If we took the roof of the raised cabin and extended it out to the sides of the boat, making a flush deck, we would get the same head room in the boat, but more actual space inside.

Is there any reason other than aesthetics why such flush deck designs are not common? They should have roughly the same windage as the standard raised cabin approach ...

I have not seen any mention of port placement and security yet. A flush high deck increases volume below, but eliminating ports cuts the perception of space, makes it less useful and less attractive.

You might say that the same amount of port space could be added to the flush deck design but those ports are much more critical because they go deep under green water just putting the rail down, even before the mast tip hits. Moving ports 'down' to the topsides makes them critical and more expensive. Thus they are often minimized or even eliminated. Without horizontal views the space below becomes far less useful underway. I would also point out that seasickness can be severe enough that crew might not be safe above, and without views of the horizons below the seasickness will likely worsen below. A seagoing boat should have a safe refuge with views of the horizons.

Personally I like flush decks from the mast forward and a nice pilothouse aft. The wimpy port lights in many production boat's raised cabins are not up to a full roll so...

 

[michael pierzga]

wehn we are talking racing - in my eye the only situation were windage is of any concern - the flush decks have another big advantage:
sheeting angle...
see the images below - do you think those tight sheeting angles would be possible on a stepped deck?

Gee...tight sheeting angles work fine on cabin tops....just put a track down. Deck sweeper tp52 headsails arent suitable for normal boats.

And with flush teak foredecks ..they may look cool ...but you need studded golf shoes to work on them


http://[url=http://postimg.org/image/a78pxbxcr/full/] subir imagenes gratis[/URL]

 

[foxy]

A lot of the examples shown are flush deck, but not raised deck like the CAL example. The flush deck is feasible when you have heavy displacement and the sole can be well below DWL or when the boat gets big enough that the freeboard is not excessive in relation to the length of the boat.

The raised deck works well with a center cockpit design such the Morgan Out Island series where it runs the full length of the boat. It somewhat masks the higher freeboard that the boat actually has.

The raised deck also works on smaller boats as a way to mask higher freeboard and gain space below. A drawback not mentioned is that boats with high bows and raised decks tend to sail around a lot at anchor. They also tend to be harder to control under power in windy conditions such as when you are trying to pick up a mooring or come into a slip.

 

[michael pierzga]

Esthetically tall topsides look...well...tall !


And since raising the deck to cabin top level doesnt create any extra headroom down below i find it not desirable.

Some small boats benefit, but in general i dont like them.

I f your thinking of a raised deck sail boat do some sketches of deck layouts and whatnot to be sure you are going in a doable direction.

 

[gmat]

I have not seen any mention of port placement and security yet. A flush high deck increases volume below, but eliminating ports cuts the perception of space, makes it less useful and less attractive.

You might say that the same amount of port space could be added to the flush deck design but those ports are much more critical because they go deep under green water just putting the rail down, even before the mast tip hits.=...

If we put the ports up near where the side meets the deck (so at the same height they would be in the cabin design, but now on the sides), we address this issue to some extent.

However, having said that, how waterproof are such ports? And does the hull material make a difference (fiberglass for example probably flexes more, breaking seals ...).

I am trying to understand the trade-off in having ports in the hull sides but high up (since it's a flush/raised flush deck).

 

[michael pierzga]

You wont have a problen with ports....recess them deep into the topsides to prevent docking damage.

Put a pad lock on them to prevent unauthorized opening by guests. Sailing with open ports ruins your day...

A recessed port in the topside directly under the lifeline gate is a very nice detail. The recess give a good toehold when boarding from. dingy or alongside the dock..

Inside the boat portholes must have curtains to block sun.

 

[dlblandjr]

A lot of the examples shown are flush deck, but not raised deck like the CAL example. The flush deck is feasible when you have heavy displacement and the sole can be well below DWL or when the boat gets big enough that the freeboard is not excessive in relation to the length of the boat.

The raised deck works well with a center cockpit design such the Morgan Out Island series where it runs the full length of the boat. It somewhat masks the higher freeboard that the boat actually has.

The raised deck also works on smaller boats as a way to mask higher freeboard and gain space below. A drawback not mentioned is that boats with high bows and raised decks tend to sail around a lot at anchor. They also tend to be harder to control under power in windy conditions such as when you are trying to pick up a mooring or come into a slip.

ahoy Foxy, Try makin up a small riding sail, like the size of a tiny spitfire, only flown "backwards" if ye will, from the back stay.
Good improvement on my boat to report, eh mate?

 

[michael pierzga]

To pick up a mooring, swing the stern into the wind directly downwind of the bouy ,then back into the bouy...you will have precise control and visabilty of the bouy at all times..

Only boats without motor need to sail bow first into the bouy

 

[Milehog]

Michael, have you considered writing a tips and tricks book?
You could name it... wait... wait... Tippy Tricks?!

 

[foxy]

To pick up a mooring, swing the stern into the wind directly downwind of the bouy ,then back into the bouy...you will have precise control and visabilty of the bouy at all times..

Only boats without motor need to sail bow first into the bouy

And then what? Do you stay moored by the stern or drag everything to the bow? Easier to pick the ball up at the bow in the first place.