What makes a good cruising boat?

On this page, we will try to share our experiences and tips on what makes a good cruising boat.

The video goes through the research we did when buying Fair Isle and our thoughts on long term cruising, including what we've learned since then.

This is a guide for getting a boat for long term cruising and sailing short handed so we are looking at strong, safe, blue water boats.

We will constantly update this page so do keep checking back. If you have useful experience of your own that you want to share, or suggestions of other points to cover, then please write in the comments section of the video. We will try to include as much of that information as possible here.

We will also talk to experts with many years experience and sea miles behind them to try to give as much information as possible on choosing a blue water boat.

 

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MORE TECHNICAL INFO ON THE SECTIONS WE COVERED IN THE FILM

HEAVING TO

When I sat down to write this after editing the video I realised I'd left out something very important from the film. The ability to heave to is one of the most important safety tactics you are going to need, especially short handed.

I would not have contemplated buying a boat to sail around the world that couldn't do this.

If you are in any doubt that the boat you're looking at will heave to, then test it! You don't have to be in a good blow to do it. Just have more sail out and make sure she will sit nicely with the foresail back winded and the rudder hard over without trying to tack or start fore reaching and gathering speed.

We didn't need to test this on Fair Isle before we bought her because full keeled boats heave to with no problems at all. The cutter rig also lends itself perfectly to this (the list of things a cutter does well just keeps growing!)

Some other rig / hull / keel configurations may require some coaxing to heave to well, but it's well worth the effort experimenting and finding a way to get it done.

On our boat heaving to is the number one go to option for storm survival. It can be done in seconds and, unless the conditions are extreme, needs no change of sails (we can use the stay sail, sheeted back hard and rolled as necessary.) Beware of relying on bits of kit like drogues that are difficult to put out and next to impossible to retrieve. They will almost certainly be being used for the first time when conditions have got very very bad as so you'll have no real idea what you're doing! If you watch Episode 2 you'll hear Rob from Zafira explaining that doing anything else but heaving to in those conditions would have been beyond what his crew were capable of doing. All the boats caught in that storm had a similar story.

 

 

Getting the boat to heave to should be as easy as tacking. Easier as you're not going to bother tacking the headsail!

 

Once the headsail is back winded sheet it flat and put the rudder hard over as if you were going to tack back and lock it off.

 

You're aiming to get the boat sitting at a constant angle to the wind in this stalled position, if you get it right things should be much more comfortable and you can get some rest.

 

Choose the amount of sail you have out to the conditions and to the balance of the boat. I would use the staysail and a double reefed main on Fair Isle in force 6 type conditions, gradually reducing sail and switching to the inner forestay and storm sail if I expected the conditions to get beyond a force 8.

In really bad, force 10 type conditions, I expect Fair Isle would sit in a heaved to position with triple reefed main and no foresails as the windage from the two rolled foresails would probably be enough to blow the bow off.

 

Experiment with different set ups to get the boat lying at a good angle, not too side on to wind and waves but not in danger of self tacking.

 

 

HOW TO DO IT

HULLS

PRISMATIC COEFFICIENT (Cp)

If you want a boat that sails well, doesn't pound upwind and require a larger sail area than otherwise necessary (with all the associated stronger rigging),  then make sure you choose a boat that has well shaped ends giving a low Cp.

 

So what is a good Cp and how do you measure it?

 

A matchbox has a Cp of 1 (square ends)

Fair Isle has a Cp of .54

The coefficient is defined as 'the ratio of the immersed volume to the volume of a prism with its length equal to the waterline length and cross-sectional area equal to the maximum cross-sectional area' and is quantified as:~

 

Prismatic Coefficient (Cp) = V/(AxL)

Where:

 

V is the immersed volume of the hull in cubic feet

 

A is the maximum cross-sectional area in square feet.

 

L is the waterline length in feet.

 

prismatic coefficient

Factors affecting the Prismatic Coefficient

The Cp thus indicates the longitudinal distribution of the underwater volume of a yacht's hull.

 

A low (fine) Cp indicates a hull with fine ends.

A large (full) Cp indicates a hull with relatively full ends.

So you are looking for a cruising boat with a Cp somewhere in the 0.5 region. For displacement hull however the best Cp is not always the lowest. Travelling at hull speed it is true that the lower the Cp the better. But if you spend a lot of time travelling at less than hull speed then a higher Cp can be more efficient.

 

You can calculate the hull speed of your boat with this formula:

 

 

Fair Isle has a hull speed of  8.6 knots (not taking into account Cp)

 

Maximum hull speed (in knots) = 1.34 x the square root of the waterline length (in feet)

The reason displacement hulls have a hull speed that takes a lot of power to overcome is this:

As the boat moves through the water it creates a bow wave that has a trough and a secondary wave behind it.

As you go faster the secondary wave moves towards the stern of the boat.

At hull speed the secondary wave will join with the stern wave to produce a bigger wave and the whole of the boat will be sitting in the trough with just the bow supported by the bow wave.

This means to go any faster you need to apply large amounts of extra power to 'climb over' the bow wave.

 

YOUR HULL SPEED ISN'T NECESSARILY THE MOST EFFICIENT SPEED TO TRAVEL AT. FOR THAT YOU NEED TO TAKE Cp INTO ACCOUNT.  SEE BELOW>

We can thank  American Admiral David W Taylor for discovering this speed / length ratio during world war one.

 

S/L Ratio

 

1.0 and below   .525

 

1.1                      .54

 

1.2                     .58

 

1,3                     .62

 

1.4                     .64

 

1.5                     .66

 

1.6                     .68

 

1.7                     .69

 

 

 

WORK OUT YOUR MOST EFFICIENT CRUISING SPEED HERE!!!

 

So we know the Cp of Fair isle is .54   Using Admiral Taylors scale we can see our S/L ratio is 1.1

 

And as the formula is:     S/L ratio =  Hullspeed /√waterline lenght (ft)

 

So:                                     Hullspeed= S/L ratio x √waterline lenght (ft)

 

For Fair Isle:                      Hullspeed =1.1 x √41.34 ..which is.. 1.1 x 6.43

 

     Therefore best cruising hullspeed for Fair Isle is 7.07knots

 

 

Knowing the hull speed of your boat means you know what your aiming at with your sail trim and on a good day you might achieve your hull speed. Going beyond that is going to take a whole lot more power and may not be possible.

Designers don't usually design their boats to be most efficient at max hull speed, at least not in cruising boats. They should design the hull with a Cp to give max efficiency at the speed you're most likely to be travelling at. Use the formula below to work out your most efficient cruising speed and have this as your default speed when motoring, you will save A LOT of fuel!

COMFORT RATIO

Yacht designer Ted Brewer came up with this formula for working out how 'comfortable' a boat might be a sea. This is working on the notion that a boat with fast reactions to wave / wind motions is more wearing and less comfortable to be in. This shows how heavier displacement boats have a kindlier sea motion. Because of the way these boats are built they are also much less likely to have hull that pounds when beating in a heavy sea. Don't underestimate the pain a lighter weight boat with a hull that is too flat in it's forehead sections will bring!

Have a look at Ted's page for lots of useful formulas... http://www.tedbrewer.com/yachtdesign.html

 

 

This is a ratio created by Ted Brewer as a measure of motion comfort. It provides a reasonable comparison between yachts of similar type. It is based on the fact that the faster the motion the more upsetting it is to the average person. Consider, though, that the typical summertime coastal cruiser will rarely encounter the wind and seas that an ocean going yacht will meet.

Numbers below 20 indicate a lightweight racing boat;

20 to 30 indicates a coastal cruiser;

30 to 40 indicates a moderate bluewater cruising boat;

40 to 50 indicates a heavy bluewater boat;

over 50 indicates an extremely heavy bluewater boat.

 

To calculate Brewer’s comfort ratio, you need to run the following formula: Comfort ratio = D ÷ (.65 x (.7 LWL + .3 LOA) x Beam↑1.33), where displacement is expressed in pounds, and length is expressed in feet.

 

Fair Isle has a CF of 47

ONE MORE IMPORTANT POINT TO REMEMBER: LIGHTER MORE SPORTY BOATS DESIGNED FOR MAXIMUM SPEEDS REQUIRE MUCH MORE SAIL HANDLING. IF YOU HAVE A BOAT YOU NEED TO REEF AT 15 KNOTS  WIND SPEED  AND AGAIN AT 20 THEN YOU WILL SPEND FAR TO MUCH TIME TENDING SAILS AND NOT NEARLY ENOUGH TIME DRINKING GIN AND TONIC!

NO, REALLY, THAT'S WHY A GREAT DAY BOAT MIGHT NOT MAKE A GREAT CRUISING BOAT. YOU'RE NOT OUT THERE JUST FOR THE SAIL WHEN YOU'RE AT IT FULL TIME AND REEFING WONT GET DONE. YOU WILL EASILY FIND YOURSELF OVERPOWERED AND WILL BREAK SOMETHING OR WORST SOMEONE!

STABILITY

There are many different formulae for stability of boats. For the moment I have left them off of this page. There are two reasons for that:

1) I have a healthy distrust of the way manufactures measure these figures.

2) Stability for a live-aboard cruising boat is very much dependent on how she is loaded. It's one of the reasons I favour heavy displacement boats for cruising. At least with these boats, if you pick one that is well designed with a good stability rating in the first place it's likely to stay that way when all your worldly belongings and enough rum to circumnavigate, is hoisted on board.

 

There is one calculation you can do yourself just with the displacement and the max beam of a boat that will give an idea. It's the Capsize Screening Formula (see below). If you're using the dry weight of a boat (a lot of manufacturers quote a figure unloaded and with empty tanks) then be aware that the real figure may be a whole lot worst. But if you're looking a a boat with proper storage low down in the boat and tanks in the keel then this figure might actually get better when loaded not worse... if however your tanks are above the waterline and you have so little storage you resort to jerry cans etc on the deck then it will be a whole lot worse!

CAPSIZE SCREENING FORMULA (CSF): Some years ago the technical committee of the Cruising Club of America came up with a simple formula to determine if a boat had blue water capability. The CSF compares beam with displacement since excess beam contributes to capsize and heavy displacement reduces capsize vulnerability. The formula is the maximum beam divided by the cube root of the displacement in cubic feet; B/Displ.333. The displacement in cubic feet can be found by dividing the displacement in pounds by 64.

 

The boat is acceptable if the result of the calculation is 2.0 or less but, of course, the lower the better.

Fair Isle has a CSF of 1.47

 

HULL MATERIAL

 

We didn't mention hull material in the video. I think this needs a video all on it's own and I will look into making this.

We did consider all materials, wood, aluminium, steel and glass when researching our cruising boat, the only thing I didn't look at was ferro cement.

Wooden boats can be a frightening proposition, but had there been a wooden boat available which met enough of the criteria for things we wanted for our boat (no boat will have everything) I would definitely have considered one.

Metal boats have some pluses and minuses. Had we had the money for a new boat I would have been more keen to look at steel and aluminium boats. But with second hand boats you can never be sure what electrolysis issues there might have been in the past and what metal wasting may have gone on. It's quite difficult to check hull thickness throughout the hull so there is always the possibility of thinning sections going undetected.

On the whole I think fiberglass is the safest option and if you can get one with vinylester  outer coating then even better.

A lot of my sailing in early years was on my father's boat which was a ketch. I've always had a soft spot for ketches and that boat was amazing, it was a sister-ship to Joshua, Bernard Moitessier's boat.

But  I have to say I have been well and truly turned to cutters now. I know I went on about it in the  video, but if you're still not convinced, here's some more reasons why cutters rock!

 

  • Unlike a Genoa you don't have to move the car every time you roll in a bit of sail to keep the sheet lead right and stop the leach or foot from flapping.
  • As you come off the wind, to say a nice broad reach, on a cutter you roll in the staysail and loosen the sheet on the Yankee which acts as a perfect reacher.  Do the same thing  with a big low cut genoa and the clew will rise and you have to take the car forward to try and keep the leach from flapping. The sail will now bend too far in and won't form a nice slot with the main. In fact it will be dumping disturbed air all over it!
  • The only reefing option you have with a genoa is rolling some in. As well as the balance problems mentioned in the video, big genoas don't roll well so it will loose shape and probably be flapping and degrading the sail cloth. Yankees roll better and you also have the option of just using a full staysail and no yankee which is equivalent to a second reef but the staysail can be all out and so can be set perfectly.
  • Full genoas often get caught by a wave when the boat is heeled which can easily damage the sail.
  •  Poling out is much better with a Yankee, you not need an oversized  pole or to roll in some sail as you do with a big genny and if you think  catching a wave  on your genoa was bad wait until you dip a pole in the blue stuff. Not something that will happen with the pole set high on a yankee.

Okay even I'm bored of hearing how good cutters are now, so here's the downside...

 

In light airs when you need to tack the Yankee may not want to go through the slot. It gets hung up on the staysail roller and no amount of pulling on the sheet will persuade it to shift.

And that's it, the only downside I can think of. Easily got over too. Just roll in a bit before coming around or take a trip onto deck and help it around. It only happens in light airs so not an issue to go for a wander on deck.

For us this very rarely happens anyway. The 9 feet we have between Yankee and Staysail seems to be enough. Obviously the closer your sails the more of a problem this will be.