Center board size

I am building a wooden, flat bottom Motor-sailor 29'8" in length with an 8' beam.

How would I determine the size of the center board I will need?

Comments for Center board size

Click here to add your own comments

Mar 08, 2013
regarding a centre board size
by: douglas hunt

i am also building a 25 ft deep vee motor sailer.

The boat is designed as a fishing type with a long keel of about 100 milimeter deep.

So, what I am doing is extending the keel to a depth of 400m/m deep for about 70% of the boat very similar to a catamaran keel then installing an inboard 21hp 3 cylinder diesel engine.

Inboard for the economical aspect and the reliability aspect.

I have also decided to build a gaff rig with a small genoa sail for sailing when conditions prevail which is most of the time this will give me a longer fishing range at low cost.

My e-mail address is should you require any assistance with your keel for your boat as there are many factors regarding the position of your mast in relation to your keel.

Dec 14, 2012
Center board size
by: Anonymous

Yes a dork style.

I am working off plans but the plans are for a motorboat and I am inverting the design to make it a motor sailor.

I have to add all the stuff you mentioned.

So where do I look for help?

Dec 14, 2012
Centre board for a flat bottom Motor-sailor
by: Mike


You say flat bottomed so is this a dory and if so is there any rocker to the bottom?

And is there any exterior keel?

I'm assuming that this board is there simply to resist leeway and heeling when under sail and not as part of the ballast?

If so then it will need to be related to the size and shape of the sail plan, though the hull shape will also have a bearing.

It’s tempting to think that keel is just a flat slab and the bigger the slab the less leeway.

However, consider it as an underwater sail which, like the one up the mast, produces ‘lift’ as the water moves across it.

And like the sail the medium it is moving through (water in this case) needs to be at a slight angle so, it works best when making some leeway (3 or 4 degrees).

Also the efficiency of a centreboard will increases with its aspect ratio, the longer and thinner it is the more lift.

On the other hand a wide (long keel) keel will give better directional stability, better for long range cruising.

The next thing to think about is how the centreboard case is going to fit in the accommodation.

The case has to be high enough for the top to be well above the waterline but it doesn’t want to be so big that it divides the cabin into two separate parts.

Also consider the amount of leverage that the keel will put on the case, a longer (deeper) board will need a stronger and better braced casing.

You will also need to allow space for the lifting mechanism.

All of which will have a bearing on the shape and size of the board itself.

So, lots of compromises.

Presumably you are working from plans?

What size and type of keel was shown in the original specs?

Click here to add your own comments

Join in and write your own page! It's easy to do. How? Simply click here to return to Your Questions and Answers.

Want to add more photos?

If you are having problems uploading Photos or would like to add more click on this link for the Upload Form.

You can upload as many as you like and there is no need to resize them.

You might like these

Recent Articles

  1. Boat Week hailed as big success

    Aug 15, 19 02:51 AM

    The Vaila Mae and Far Haaf in Lerwick Harbour. All photos: Shetland Amenity Trust/Shetland Boat Week

    THE ORGANISERS of Shetland Boat Week have hailed this year’s event as the most successful yet.

    Over 500 people flocked to Hay’s Dock in Lerwick each day during the family-friendly event, which took pla…

    Read More

  2. Neil Pryde Small Boat Sails

    Aug 15, 19 01:15 AM

    Neil Pryde (Formex) Main Sail 42 sqft, Marconi - Luff: 11' 2 and 7' 10 foot. Either Red Stripe on white with white Scamper 60 graphic or yellow & white

    Read More

  3. UL education counselor and granddaughter build sail boat together

    Aug 14, 19 04:50 AM

    © Provided by Irv Esthers Irv Esters and his granddaughter Arya Esters pose for a photo in the middle of the boat they built together.

    If there's one thing Irv Esters enjoys more than sailing, it's hanging out with his only grandchild.

    Over the last six months, the University of Louisiana Lafayette department head of counselor educati…

    Read More