Speed is important, it can get you out of harm’s way, and it makes sailing much more fun, but figuring out how fast a catamaran will be able to sail can be tricky. One important aspect is to understand maximum hull speed.
In this article, I have calculated different hull speeds for different lengths of boats; this includes both monohulls and catamarans but focuses on the latter. Here is the catamaran maximum hull speed table:
Catamaran Max Hull Speed Calculator Table
|Length on Water||Displacement|
Max Hull Speed
Beyond Max Hull Speed
- Length on the waterline (L.W.L.): Length of the boat when measured on the waterline, not to be confused with length overall (L.O.A.), which is the boat’s total length (above the waterline) including bowsprit, etc.
- Displacement max hull speed: The max speed of a boat whose L.W.L doesn’t change when underway and where the vessel’s bow wave is the limiting speed factor.
- Semi/Light Displacement or Semi planing hulls speed: A boat where the bow waves speed limiting factors can be partially overcome and therefore exceed the displacement hull speed. These hulls usually overcome hull speed by 10-30%.
How to use the Catamaran Hulls Speed Table
- Choose your length on waterline in the left-most column, either in feet or meter.
- Continue reading to your right and stop either at “Displacement hulls speed” or continue to “10,20, or 30%”, depending on your estimated hull efficiency. This will be your calculated maximum hull speed for a semi-displacement catamaran.
First of all, we need to know the maximum hull speed for a displacement hull, and from that number, we will be able to calculate how much faster the semi-planing (or semi-displacement) hull will be. This is the formula for Maximum Hull Speed on a displacement boat:
Max hull speed= √((Length on Water Line x g) /(2 x pi)) x 3600/1852
Now we need to add the increased efficiency (loss of drag) of a semi-displacement hull, usually, this is somewhere between a 10-30% increase.
Semi Displacement hull speed = Maximum hull speed * 1.3
Note: “1.3” is the increase in efficiency, if you believe you are on the lower end of the scale this would be 1.2 or 1.1.
How to Exceed Hull Speed
This calculator offers a theoretical perspective, but many other factors such as sail plan, weight, and sailor skill, of course, have a profound impact on speed. As we have seen, a semi-displacement hull can exceed maximum hull speed, but we can also see that it isn’t by much. The next step is to reduce drag even further by utilizing a planning hull.
If you want to better understand catamaran speed I suggest you read another one of my articles called Catamaran speed explained.
Catamaran Hull Speed Spreadsheet
If you want more info, calculate other lengths or see the speeds in Km/h or Mph then I suggest you check out this free spreadsheet.
Note: If you want your own copy just click, File->make a copy.