Elan Impression 40 LWL

cmedsailor

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Elan impression 40, which uses the same hull as the previous impression 394, which uses the same hull as the previous impression 384 (!) has a waterline of 10 meters only. How can a boat which is nearly 12m long can, nowadays, still use a hull with so short waterline length when all rivals have at least half a meter of LWL more?
Despite what I mentioned, has anyone sailed one of these models? Are they indeed slow in comparison to competition (Bavaria 40, Jeanneau 409, Beneteau 40 etc) due to the smaller LWL or has Rob Humphrey found another way to make them fast?
 

doug748

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Maybe the odd half knot on the maximum speed does not have much sway in that sector of the market. It might, people buy stuff on all sorts of rum ideas

As you say, the Humphries boat may well be nippier anyway. Here is a boat with a similar waterline to the Elan:

http://sailboatdata.com/viewrecord.asp?class_id=7274

We all know which is the better racer, for waterline is only one factor and, for example, if the boat carries modest canvas it's maximum theoretical speed is irrelevant much of the time.

If RH felt he could produce a slippier profile and minimise wetted area whilst reducing ballast, excessive sail area, and incorporating a less draughty/draggy keel; he might feel he had got the best of the deal. Especially as the boat would still have a modicum of increased LWL when heeled.

It's all conjecture of course. What Elan did was scratch their bums and said something like:
"It's a good hull, still up with the competition, we can get a few more years out of it, lets go for it"
 
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lpdsn

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or has Rob Humphrey found another way to make them fast?

The Impressions don't give the impression they were built for speed (if you pardon the pun). If you want a faster Elan you'd be better off going for their cruiser racer range.

The main driver for long LWL in cruising boats is that it gives a higher STIX figure. Presumably the Elans can achieve a high enough figure to get the appropriate RCD category without having to use every last inch of waterline length.
 

cmedsailor

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To the OP - LWL only affects maximum speed, what percentage of your sailing is at hull speed?

Agree that the maximum speed in knots of a displacement hull (hull speed) is: 1.34 times the square root of the waterline length in feet, BUT, I cannot understand how come and it's only the maximum speed that is affected. I mean, why not all speeds for the same wind speed (or engine rpm) or whatever. OK, you got me confused now....
 

Tranona

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"Hull speed" is just a construct that describes the point at which a significant increase in power is needed to overcome wave resistance and go faster. It is not absolute and the factor (variously between 1.3-1.5 depending on who you read) is only an estimate. It varies according to hull shape, WL area etc. The only constant is that as LWL increases so does the point where the distance between bow and stern wave exceed the LWL. You notice this when the bow is trying to climb the wave and the stern squats.

You can usually achieve this point if the power of the engine is such that the change point is easily achieved, but often can be easily achieved under sail by over canvassing on a shy reach - you know those brown trouser moments sometimes followed by a broach.

This does not really answer your question. Maximum hull speed related to length just estimates the potential and does not necessarily translate directly into faster passage times. In the latest designs the greater LWL is primarily to increase the amount of parkable boat length that can be used for accommodation. On some boats this additional length is used for a bigger cockpit, on others for a larger cabin - the extra speed potential for most is a bonus - probably not used because of modest SA/Disp ratios.

The Elan Impression was designed at a time when shorter LWL was more common, plus a very modest rig reflecting the relaxed cruising style it aimed at. Similar to my old Bav 37 which had virtually the same LWL, displacement and sail area as my new 33. The extra 4.5 ft hull length was all in the raked bow and sugar scoop stern - the cabin and cockpit length are virtually the same.

As to your main question, doubt the 0.3 difference in potential "hull" speed will have much impact on normal passage times. You need to look at the other data - Displ/LWL to see how heavy the boat is, and SA/Displ to see how much power is available to shift the weight to get an idea how easily the potential can be utilised. The magic bit is then trying to assess how well the boat can deal with the conditions you are sailing in - plus of course your ability to make use of all this! No doubt Rob Humphries in the Elan would run rings round Joe Bloggs in one of the other boats you mention.
 

cmedsailor

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Stick to the brand you know and love, Phiippos, far better allrounder :)

Ha, ha, I was expecting it that you will come around and mention something like this!!! No, I am not interested in the Elan (although a year ago I made a long delivery trip of 650 miles with the Impression 45 and I was really impressed; but that's another beast). I was only looking, on the internet, at various 40-41ft boats and this big difference in the LWL in comparison to rivals really made me wonder. Enjoy your Benny. I still really love my 361.
 

lpdsn

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Agree that the maximum speed in knots of a displacement hull (hull speed) is: 1.34 times the square root of the waterline length in feet, BUT, I cannot understand how come and it's only the maximum speed that is affected. I mean, why not all speeds for the same wind speed (or engine rpm) or whatever. OK, you got me confused now....

There are various components to the resistance of a yacht. At low speed, frictional resistance predominates, so wetted surface area is the main factor. At higher speeds the main factors is the bow and stern waves generated by the forward motion. Hull speed is the speed at which the wavelength of these equals the LWL. It is no absolute barrier; just at that point the amount of power needed to go faster is pretty high so very few displacement boats or ships are designed to overcome it.

And that is only in flat water. There are quite a few other factors, such as energy lost generating waves when pitching (I suspect the Impression and other tubby AWBs won't score that well on that point), induced drag on the keel and rudder when they're providing lift, and a few others.

You can buy quite weighty books on the subject, with which I'm neither willing nor able to compete.
 

roblpm

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Elan impression 40, which uses the same hull as the previous impression 394, which uses the same hull as the previous impression 384 (!) has a waterline of 10 meters only. How can a boat which is nearly 12m long can, nowadays, still use a hull with so short waterline length when all rivals have at least half a meter of LWL more?
Despite what I mentioned, has anyone sailed one of these models? Are they indeed slow in comparison to competition (Bavaria 40, Jeanneau 409, Beneteau 40 etc) due to the smaller LWL or has Rob Humphrey found another way to make them fast?

OK at risk of getting flamed for reviving a 4 year old thread...............

Can anyone confirm the fact that the 384, 394 and Impression 40 are the same hull? How do you know?

I am a pauper and am thinking about a 384 for Med/Caribbean liveaboard. 2 people only. Sailing Avalon sailed one to Australia and didn't die which is my main criteria. Actually my other criteria is good in hot weather. I will have sat weather forecasts and am a fair weather sailor.......

Sailboatdata has an incorrect displacement/length ratio for the 384 I think which makes it a super lightweight at 154. The 394 is in at 222 which is more like what I am looking for. No racing. I think this is because there is no LWL quoted in the 384 brochure.

Bonus points for anyone who owns or has sailed one on fitting decent under deck AP linear drive.
 
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