We learned a long time ago that the key to happy cruising is a smooth ride uphill. Careful weather routing and a good turn of speed reduces your exposure, but those inevitable rough upwind passages are what people remember when it’s time to cast off the docklines. This is why we’ve spent the past 40 years working on the wave piercing bow, which is particularly effective when heading into wind and wave.
There are numerous posts on the subject of wave piercing on SetSail (listed at the end of this article), but for now we want to show you photos taken over the past four decades. This first series is of FPB 97-1 in 30 to 34 knots of true wind speed, making 12.5 knots into a three to occasional five foot chop.
With a 107-foot waterline and a fine entry you would expect a clean slice through the wave.
At the other end of the historical record is Beowulf VI, a 38-foot cat that in 1975 had what may have been the first wave piercing hulls. Going to weather she would slice her leeward hull so cleanly through the seas that you would not feel any motion or deceleration, until the main crossbeam was impacted.
Uphill is even less fun with a monohull sailboat; however fine entries, balanced lines with heel, and moderate beam sterns, like those of the Sundeer 64 above, make the endeavor far more comfortable and efficient.
Here is the FPB 83 prototype Wind Horse going uphill ten years ago in similar conditions to the most recent FPB 97 photos. Notice how she splits the wave.
The size of FPB 97 Iceberg diminishes the appearance of the waves. In scale she is knifing through in the same fashion as Wind Horse.
Now an FPB 64. Smaller yachts typically have a more difficult time piercing the waves. But the FPB 64, as you can see in the photo above and below, gets the job done.
Here are a few links on wave piercing and weather discussion :
https://setsail.com/heavy-weather-issues/
https://setsail.com/wave-piercing-and-axe-bows/
https://setsail.com/pitching-in-headseas/
https://setsail.com/wave-piercing-design-in-action/#more-5783
For more information on the FPB series, contact Sue Grant: Sue.Grant@Berthon.Co.UK.
Posted by Steve Dashew (May 8, 2015)
May 8th, 2015 at 8:08 pm
Steve,
I may have this wrong, I haven’t rechecked the various images you have published of the underwater bodies of your FPB series boats and I am working from memory, but it seems to me there has been a change in underwater body shape from Windhorse through to the latest of the breed. It seems to me the underwater bodies have become progressively deeper and the bilges slacker. Is this correct? If so, it seems counter intuitive, particularly for a high performance power boat. I would imagine slack bilges might reduce roll resistance and control, something you obviously place great store on given the sophisticated devices you use to effect such control. If this trend is correct, is it designed to allow better wave piercing behaviour well up to amidships? And if this is the case is there then a trade off between roll control and wave piercing performance?
On the matter of roll control, and I apologize for the diversion from the theme of your post which is wave piercing and pitch control, I was wondering whether you might comment on the following. You effect roll control with a stabilizer on each side of the hull. Given that the stabilizers are more vertical than horizontal, when in operation, do they impact steering control, given they are located somewhat off the centreline? I was also wondering whether one articulated fin (need not be too deep), hung off the back of a small keel (or perhaps no keel, just the rotating fin) could do the same thing effectively? Located at or near the centre of turning (longitudinally) in the hull, it would have minimal impact on steering control. It would be more efficient, there being only one stabilizer doing the work of two. The draft would be impacted, but I note that Windhorse had a keel anyway. It would probably not work with the hull shapes evident in the later designs (that’s if I have this correct). Make any sense?
Thanks.
May 8th, 2015 at 8:28 pm
Thoughtful observations and questions Henry:
Regarding the development of hull shapes, there has been refinement in our forward sections based on the tradeoff between steering control, upwind motion, displacement and stability. This is a process that is complex, based on a mix of science/engineering, seagoing experience, and intuition. Stabilizers can indeed produce a steering force as well as a heeling (or counter heeling), while rudders produce a heeling as well as turning force. Correct placement of the stabilizer fins will mitigate or eliminate the steering component. The optimum location varies depending on many hydrostatic factors. In our case we like to be fairly close to the longitudinal center of buoyancy. Depending on hull shape, a single centerline stabilizer fin could be effective, and in some cases be substantially more efficient than a pair of foils. However, that draft increasing foil would substantially increase draft and be vulnverable in a grounding. If you are not concerned with draft, then it would be worth considering.
May 15th, 2015 at 12:29 am
Steve,
I guess the difference in displacement between the FPB83 and FPB78 necessitated a deeper canoe body and no keel so as to maintain draft below 5′?
If the stabilizer foil was behind a keel (if draft is not a consideration) then it would be better protected, but then again the athwartships stabilizers are exposed in any event, so there is no real difference (other than draft). If hung from a keel, then there would also be no problem slipping the vessel?
Have you ever considered using water jets instead of foil stabilizers, say, ejected laterally from a shallow keel? It could be part of a bow thruster system also.
May 18th, 2015 at 10:39 pm
Hi Henry:
Right now there isn’t time to go into the variations in hull design. We used water jet thrusters in the early 1980s and they were not very successful. We have not seen anything since to change our minds.