January 25, 2023 - Everett, WA- Nabla Bulbous Bow

 January 25,  2023 - Everett, WA- Bulbous Bow 

While at Van Isle Boatyard, our project manager was able to put us in contact with the naval architect who designed the bulb on Raven - Pat Bray.  We were able to learn more about the the design which is a more substantial bulb than the production design.  He sent us the schematics along with information regarding their benefits.  

Based on our observations of Ravens performance it seems we are enjoying many of the benefits he describes (see below).  For example, when comparing Raven to other similar Selene's, cruising at the same speed, we have a lower fuel consumption rate.  While the power plant and propeller may play a part in the difference, Pat Bray claims the biggest factor is the bulb.  

Raven -Bray Marine Nabla shaped flooded bulb

The following information has been provided by Pat Bray:

Nine Things You Need To Know About Bulbous Bows

A bulbous bow will:-

1 Be even more effective in reducing resistance once you get above hull speed. People think of bulbs only for displacement hulls where in fact a bulb starts to work most effectively once you approach hull speed, and reach their most effective above hull speed. At 20 knots a typical 45m (147 footer) will use 2,100 less hp because of a bulbous bow.

2 Reduce your trim angle by almost 1 degree, improving visibility.

3 Reduce your pitching motion significantly increasing comfort and improving seakeeping.

4 Lower the height of your bow wave, reducing water on deck and environmental impact.

5 Increase your range under power from 12 – 15%.

6 Reduce your fuel consumption up to 20% depending on the vessel speed.

7 Mean that in a new build vessel you can fit an engine with 20% less hp and have fuel tanks 12-15% smaller and still reach you contract speed and range.

8 Reduce your Gross Tonnage by reducing hull volume because of smaller fuel tanks making for a lighter boat.

9 work very effectively as an ice breaker bow on new ice.

Who knew?

We have retrofitted bulbs to over 50 boats, as small as 40 ft. and as large as 150 ft. and speeds up to 24 knots. We have done extensive model testing on numerous designs from deep V hulls to lobster hull forms. If you are interested in learning more about the advantages of bulbs and other hull-enhancing appendages, contact us for our paper on F.A.S.T. Hull Technology. pat@brayyachtdesign.bc.ca