How does Whio do it?

Hi gang,

So I am experiencing a dilemma, how is it that Whio, a well-known and beloved wooden semi-displacement hull, manage to only weigh in at 2800lbs. I find the weight listed from OffCenterHarbour a bit hard to believe.



I understand that having a crazy big blade that was custom made for the boat lets it be extremely fuel-efficient, and the speeds are possible due to the low weight. But how is it that this 29.5' long, 7' wide, boat only weighs 2800lbs while Paul Gartside's "Wayward" comes in at 3000lbs and is only 24', 6.3' wide? Gartside Boats | 24 ft Launch "Wayward", Design #119 https://store.gartsideboats.com/collections/power-boats/products/24-ft-launch-wayward-design-119



Both boats are absolutely Spartan and have high L/B rations. But I just cant believe the 2800lbs number for Whio. The difference is 5' in length and 1' in beam, that's a lot of extra material, also considering the Wayward has a tiny 25hp outboard and Whio has a 50hp inboard diesel.

Can anyone offer some insight, and if you think the numbers are wrong, how much do you think Whio actually weighs in at?

Woops, just did more research and found that offcenterharbours kit design comes in at 3600lbs, something much more believable.

AROHA - Plans & Kit Ordering Page - OffCenterHarbor.com https://www.offcenterharbor.com/plans-och-aroha/

Displacement not equal weight. Of course, generally, not less.

The sign for imperial feet is a single apostophe and the double represents inches.

29 feet is 29', the difference in beam is 7'-6.3' or 0.7' and 5.5' in length

0.7' is the same as 8.4"

I haven't looked at the scantlings or structures of either boat but the Aroha is really small. Look at the two from above...one carries her beam to the stern. The other doesn't. And who knows what's been included in the displacement weight. Designers set displacement weights based on what their expectations are for the boat are to get her to rest on her intended waterline... maybe it includes a pilot and a ham sandwich, maybe it includes enough fuel to go offshore and four fishermen and tackle.

I could see a careful builder getting the Aroha under 3000 pounds, for sure.

fallguy said:

Displacement not equal weight. Of course, generally, not less.

The sign for imperial feet is a single apostophe and the double represents inches.

29 feet is 29', the difference in beam is 7'-6.3' or 0.7' and 5.5' in length

0.7' is the same as 8.4"

Click to expand...

Indeed you are correct good sir, I edited it accordingly. Thanks for the catch

cracked_ribs said:

I haven't looked at the scantlings or structures of either boat but the Aroha is really small. Look at the two from above...one carries her beam to the stern. The other doesn't. And who knows what's been included in the displacement weight. Designers set displacement weights based on what their expectations are for the boat are to get her to rest on her intended waterline... maybe it includes a pilot and a ham sandwich, maybe it includes enough fuel to go offshore and four fishermen and tackle.

I could see a careful builder getting the Aroha under 3000 pounds, for sure.

Click to expand...

You bring up some good points, I think the folks at OCH were more pragmatic and accurate than the designer of Whip was.

Thanks for your input.

28mpg @ 7.5kt ?? That sounds pretty good. It makes me wonder what a purpose built 45' craft of similar concept would do if built as light as possible with fiberglass and PVC foam and proper displacement hull form. The Willard line of trawlers were some of the most efficient I know of, and they used conventional single wall (heavy) fiberglass hulls and also were short and relatively fat for their length. They also had ballast in all cases that I am aware of.

On page 278 of the book "Fiberglass boatbuilding for amateurs" by Ken Hankinson, there is a picture of a sailboat hull that is finished inside and outside with stanchions for lifelines that weighs under 700lbs (40' oal). The hull is made from foam and primarily UD stitched fabrics, vacuum bagged.

hmmm, that is quite something I must say. Ya I guess I'm building my amateur intuition of reasonable weights for wooden hulls. I understand that fiberglass is in a league of its own. That's why I found it hard to understand that two wooden boats would have such a large weight difference, with the larger one being lighter.

I understand that the original Whio was reported at 1100kg (2425lbs) with empty tanks. It's no problem to achieve that weight with cold molding on laminated frames. The kit version weighs more for sure, they use meranti ply for frames, bulkheads, and planking.
The weight difference to other boats has to do primarily with the designers ideea of how close to the lower limits of the possible scantling he wants to go.

For a 29 1/2 feet canoe, it is pretty heavy. I worked building 30 feet canoes, of only 4 feet beam with only seats that weigh 200 Kg (440 lb). They could be lighter but are used to carrying 13 people.