Albin-25 "Displacement" or "Semi-displacement" hull?

[NickScheuer]

This may sound like a dumb question, however, I recently converted from sailing a Yawl to motoring in an Albin-25 and have next to no experience with Power Boats.

When I became interested in Albins it was because they had a comparatively small, economical Diesel engine and assumed they had "displacement" hulls. However, After snapping a photo of our wake a month ago while moving at about 10 knots, I suspect that we were "on plane", and perhaps Albin-25's are more properly classified as Semi-displacement".

Opinions from the more experienced among the AOG?

Nick

[joe.baar]

Can we see the photo? Please post it.

Once again, the formula to determine your maximum displacement hull speed is 1.34 times the square root of the waterline length. This is true of all watercraft. Any speed you're making through the water - not necessarily over the ground, as in calculated by a GPS unit - in excess of that calculated one, means you're planing or trying to. A true speed of 10 knots, measured by some kind of log, on a boat 25 feet "length on deck", must surely be a planing speed for that hull.

Take care on the water.

[hetek]

I'm not an expert on the A25's (I own a A27FC), but it is my understanding that an A25 built before 1973 was a true displacement hull. In 1973-74 Albin reworked the hull design to give it more of a flattened hull aft which aids in planing. I guess you would call this semi-displacement then. These later models were called "DeLuxe".

My A27 is semi-displacement and also has a flattened hull bottom aft. 27's have been known to hit 14 kts and more, providing there's enough power.

And I have to agree with Joe - I would love to see a picture of an A25 doing 10 knots. I can only dream. My A27 "only" hits 8.5 knots with the Lehman 61 hp.

- Jon B.

[leprof31]

I think you got the answer. I believe 1973 is the year for the new hull design. Mine is a 73 and have the deluxe volvo penta 36 HP, MD3B.
And I went over 10 knots some time... once, I was going back from Quebec to 3-Rivières with the tide and the wind on my side... I was running around 11 knots, but it was very windy. And two times at least, cruising from Trois-Rivières to Québec, in the Rapid Richelieu, between Deschaillons and Portneuf... but the current in the rapid can go up to 6-8 knots sometime; imagine going on the way Portneuf/Deschaillons against tide... lucky if I get 1 knot of speed

[NickScheuer]

Opps! Forgot that the GPS unit used reads Miles Per Hour, not Knots. When it reads 10, the numbers translate to 8.6 knots. Might'ta wrote "knots" just because "MPH sounds out-of-place in reference to boats.
i

[glk34]

Great, 8.5kts sounds possible. I thought I must have a much slower A25 because about 7.8kts ties old 1970 Iron Jack up. I was always under the impression that the A25 was a semi displacement hull. While they will come up somewhat on the bow, I do not believe they actually ever get up on plane. Even to get above 6.5 kts with a water line our length means they must come up a bit. A true displacement hull at 25ish feet would never get to 8kts (unless surfing down a large wave). I never heard of the deluxe difference in planeing ability before but thats what is so great about this forum-you can learn things every time you come on.

Iron Jack

[NickScheuer]

One point worth mention here: My 1976 DeLuxe has a subtle concave "recurve" on her run (bottom) throughout the trailing 18" immediately forward of her transom. It appears to be about 3/8" to 1/2" deep.

The line drawing published in my Albin-25 Handbook (old and dog-eared) does not show this "flare" feature, so maybe it was an improvement incorporated sometime during the years of production prior to 1976.

[hetek]

Good point Nick -

I didn't know the 25's had that also. I thought the "hook" was exclusive to the 27's. My 27FC has it too.

Rumour has it that it was unintentional and it was actually caused by the hull mold warping while curing. It does have a performance benefit and acts like a crude trim tab for the semi-displacement hull.

As the painter Bob Ross would have called it: A "happy accident" in the manufacturing process.

Now where should that happy little tree live in our happy little world?...

I miss Bob.

[NickScheuer]

"Acident" of the molding process is difficult for me to bielieve, Jon. The pair of fiberglass-sheathed laminar flow leeboards I made for my Shearwater Yawl had just such a feature on their high-pressure sides (corresponding to the underside of an aircraft wing). The foil section was designed by a fellow nmed Tom Spear.

The leeboards met my expectations for lift to windward and for low-drag.

I'm sure the "hook" (is that the best term?) is intended to optimise the hull's performance in "Semi-Displacement" mode. I immediately appreciated that feature when discovering it the first time we looked at the Albin-25 prior to purchase.

[hetek]

Hi Nick -

Only know what I read... Here's one I found:

viewtopic.php?f=28&t=1493&start=15

The last two posts may describe it better than I did.

"Hook" is the proper term to describe a power boat hull. It refers to a concave portion of the hull bottom just forward of the transom and indeed acts as a crude trim tab. Most designers avoid using a hook in the bottom saying it is a poor solution for improper hull design. Please remember, I'm talking true planing hulls here. The opposite of "hook" is "rocker" and it is just that - a rounded bottom in a bulge type form. Again, not good for a planing hull as it causes ineffiencies in the planing hull's hydrodynamics. It also can make the hull porpoise (bow bobbing up and down while on-plane).

It used to be that the best planing hull was straight-edge flat, for the last 1/3 of the hull bottom, forward of the transom. This is where the planing powerboat contacts the water when on plane, at speed. Powerboat racers actually blueprint this area of the bottom. Nowadays, stepped hulls seem the norm, but that is another story.

As mentioned in that thread, and several others I've seen, Joe Puccia was the designer of the 27. Per Brohall was the designer of the Swedish Albin 25.

Your observation of your 25's hull raises some interesting questions: Why does Joe P. say the mold warped (assuming he was talking about his 27 design), but Per B's 25 also has the same feature? Or did Joe P. have a hand in the "DeLuxe" version redesign of the 25 and that is when the hull warped? And maybe he found that the hook had an added benefit so he incorporated it (on purpose, this time) into the hull design of the 27?

"Hey, if it worked on the 25 then why not use it on the 27?" ... I'm just thinking out loud here.

Powerboats are a different animal than sailboats. It also seems that Albins are a different breed than your typical powerboat. That's one reason why I like them.

[dab1066]

Aloha, does anyone here know the GPH at displacement speed for Albin 25 or 27? let me know. Mahalo