Daggerboards on Catamarans: a Guide

What are daggerboards for on catamarans and how do they differ from mini-keels? This is part of our series that includes catamaran travellers and points of sail on a multihull.

As with everything on boats, there are advanatages and disadvantages to both and some compromises to be made.

If you strip this down, daggerboards control one thing: how your boat converts wind force into forward motion instead of sideways slip (leeway).

Everything else, speed, pointing angle, safety, handling, flows from that.

A catamaran without boards is less complex but will not point as high, especially in lighter conditions.
A catamaran with daggerboards allow you to actively tune the underwater shape of the boat in real time.

Think of your boards as your underwater sails. Trim them well and you will maximise your VMG (velocity made good).

In Plain Terms

Step-by-step reasoning

Wind on the the sails creates a sideways and forward force.
The hull alone cannot resist sideways motion effectively.

Daggerboards act like underwater wings (foils) and resist sideways movement.
As water flows past them, they generate lift sideways, fighting agaianst leeway.
The result: more of the wind force turns into forward speed.

More board = more grip (lift) but more drag

Less board = less drag but more sideways slip

That trade-off is everything.

Daggerboards vs Mini-Keels

Daggerboards (Performance Cats)

Why they are faster

Higher aspect ratio foils generate more efficient lift

You can retract them to reduce drag

You can adapt to the conditions.

The impact

Your pointing angle improves from around 55–60° (mini keels) to ~45° to the true wind direction,
Reduced wetted surface = higher speeds off the wind

The Downside

More complex
Impact vulnerability (mitigated by crash structures)

Mini-keels (The Cruising Compromise)

This is a more simple solution and a very good one. The perfromance difference between boards and keels reduces as the wind and sea state pick up.

• Simplicity: no moving parts
• Protection: mini-keels shield rudders and saildrives
• Easy grounding and maintenance

The Cons of Keels

• More drag
• Lower upwind efficiency (more leeway)
• “Train track” steering off the wind

Other Critical Concepts

The “Tripping” Risk (Safety) with boards

A Deep leeward board acts like a fixed pivot
If the boat loads up in a gust or wave, the hull stops, rig keeps moving increasing your capsize risk

The solution is to raise the leeward board in strong conditions

You don’t want your boat “hooked” into the water when loads spike. This gives you a good way of reducing loads on your rig in strong conditions, but it does add complexity.

The “Ice Rink” Effect (Control)

This is an important consideration on a daggerboard cat when you start to sail further off the wind.

• No boards down = no lateral grip
• The boat may slide unpredictably
• Rudders overload, autopilot struggles

The Solution is to maintain 20–30% of your boards down going downwind to give you just enough grip for directional stability.

How to Use Your Daggerboards

Boards are not “up or down”. They are continuously adjustable controls, like sail trim.

Note that these numbers are guides. Each boat will be diffferent, so play around and fine tune your boat accordingly, but these will give you a useful starting point.

Upwind (Beating)

Light wind (<10–13 knots)

Leeward: 100% down
Windward: 100% down

Generally speaking, in lighter conditions, it is better to have too much board down than too little. Maximise your anti-leeway in these conditions.

Medium wind (13–20 knots)

Leeward: 100%
Windward: 75%

You are now generating more lift thanks to the speed f the water over the foils so you can afford to reduce your drag. Take some board in.

Strong winds

Leeward: 0% down
Windward: 100% down

In stronger conditions, loads increase
A full leeward board creates a big leverage and increases your tripping risk.
Once you have reefed, you may be able to set your boards more agressively
Raising your leeward board gives you a good safety margin.
And you reduce your drag.

Gusts / Squalls

Leeward: raise quickly

This is a useful way of reducing the load on your rig if you are slow to reef your sails.
You achieve an immediate reduction in side force which minimises the risk of tripping
It’s like putting in an “underwater reef”

Beam Reach

As you come off the wind, you can gradually raise your board and reduce the drag. You don’t need so much force to counter the leeway.

Leeward: 50%
Windward:50%

• You still need some lateral resistance, but not full lift
• Reduce your drag to increase speed

Broad Reach, Downwind

Leeward: 25%
Windward:25%

Continue to raise your boards, but keep some in the water for steering control and to prevent yawing. Having some board in the water also protects your props.

Storm Conditions

A useful safety aspect of daggerboard cats is the ability to raise them fully in strom conditions. This allows you to slide down the waves. Keep some board out if you are following the weather, surfing down the storm. Throw a drogue or some warps off the transom aft to help slow you down.

Boards: minimal (0–10%)

Too much board = risk of tripping
Too little = unstable steering

Balance is key.

Match your Boards to your Sail Power

This is key.

As you reef your sails you should also adjust your boards to keep the boat balanced.

Other Insights

There are various types of boards that you will see on perfromance catamarans such as the Curved daggerboards you will see on a HH44, to angled straight boards you will find on a Gunboat. Some are inboard (Windelo), some towards the edge of the deck (Outremer).

C-Boards will generate more vertical lift (eg up to 500 kg lift at 15 knots)
This helps to reduces displacement, reduces dragm increases speed. Angled boards also achieve this to a lesser extent. The Gunboat 68 goes down this route as they believe the differece is marginal.

There is a trade off with “C-Boards”. They are more complex, more expensive and harder to ship around the world if you need a replacement.

Rememeber also, that raised boards above the deck increase your windage. That’s another trade-off.

Mark your Lines

You can’t see your boards underwater, so:

Use markers on your lines for 25%, 50% and 75% down (some vcats may have markers on the boards).
Use the lifeline height as reference

Mistakes to Avoid

Leaving both boards down all the time
You are maximising your drag. Generally, you only want to do this upwind in lighter conditions.

Sailing downwind with no boards
This places stress on your autopilot and is inherently unstable

Keeping leeward board down in heavy conditions or gusts
This increases capsize risk

Not reducing boards as speed increases
This results in excess drag and structural load

Not raising your boards as you come off the wind
Reduce your drag as you sail at deeper angles.

When Keels ar the Best Choice

Daggerboards are not always the best solution for everyone.

Go for mini-keels if:

You prioritise simplicity
You frequently beach or dry out
You sail in debris-heavy waters
You don’t actively trim systems

If you don’t adjust boards your properly, keels can be more efficient in practice.

For sailing efficiently upwind however, boards always beat mini-keels, especially in lighter conditions.

At the Marina / On Anchor

Final Thoughts

Daggerboards turn a catamaran into two completely different boats:

Boards down- you have an efficient, precision upwind machine
Boards up, you have a low-drag high-speed surfer

If you treat them like fixed keels, you lose most of their value.
If you trim them like sails, you unlock the full performance and safety envelope of the boat.

BUT, they are more complex and come with more responsibility. Trim your boards according to the wind direction, stregth and sea conditions.