Extending a Lagoon 40

[EngineerRetired]

Originally Posted by Factor

Yes Way

You'll have to show me the numbers, including the loss of market value once modified.

[fillintheblank]

Originally Posted by EngineerRetired

You'll have to show me the numbers, including the loss of market value once modified.

I will guess that Colin will have 1500-2000 in his extensions, and that is he bought it all just do it no left overs from other work. And I am including peel ply, the formica he used for the form etc.

His labor is free to him, and I would guess he will have 100-150 hours in each one by the time its complete. So he will have 5-7k invested if you paid him for his hours. Can you sell a boat and buy a bigger one in the same condition 5-7 k more?

[Factor]

Originally Posted by EngineerRetired

You'll have to show me the numbers, including the loss of market value once modified.

Using Seawind 1000 as a benchmark Standard 1000 in top notch is May $200-220K, an 1000XL in similar condition is 250-255K AUD at the moment. Stretched Boat is maybe $220 - $240K and cost to stretch is $20K or less. As you chaps say, do the math(s). So in effect you get the job for free and get 10-15% better performance and improved ease of use along the way.

And of course that cost is based on using the highest quality available professional, if you can do it your self, even more savings

[spiv]

Originally Posted by Simi 60

Why didn't you follow the line?

I did follow the gunwale curve, you will see it when I post a pic from the outside.

[spiv]

Originally Posted by Cadence

Question, how is it tied into the hull structurally?

Two layers of 450gsm DB Eglass, 25mm PVC foar and 1 layer 450gsm glass inside.
All hi grade epoxy.
I can lift the boat from there.

[spiv]

Originally Posted by jmh2002

That's starting to be a more useful type of transom size for dinghy boarding, swim platform, fishing, diving, etc

..... And that's without even mentioning any of the performance or handling related aspects when underway.

But I understand why, and that for the manufacturers it's actually about minimising length, for marinas, for perceived size brackets of potential owners (who may baulk at a 50ft LOA, even if it's really a 40 something footer in volume), etc, and about creating the maximum volume within that minimised length.

Of course that is that total opposite of what makes a good multihull, which is to be long, slim, and light, relative to other factors.

I totally agree with all your statements.

[spiv]

Originally Posted by EngineerRetired

No way is it cost competitive with moving to a bigger boat.

When did you last check the price of a Lagoon 380 and a Catana or Outremer 45?

More space inside in the Lagoon, but fat and short, so a few dollars in PVC foam and fiberglass and my time make a lot of sense.
Even spending 20k from a professional still makes a lot of sense.

[NSfooter]

Speaking as a Naval Architect, there is only one sensible way to add length - in the stern. This is for two reasons. Primarily as you need to keep the lines fair and the bow is already a point, so extending the bow would mean the lines were no longer fair. A midship "plug" would most likely not be fair either, because sailing boats don't have parallel mid bodies, like cargo ships. Adding stern extensions, if designed properly, will give you fair lines. I'm not familiar with the L40 lines, but you may find that to have a faired extension on the stern, the transom at the design waterline is out of the water, in which case giving you nothing in terms of waterline length, except if you are heavily loaded and/or pitching in a seaway. Secondly, a stern extension would be subject to the least stress. Midships would be the highest in terms of bending moment and shear forces. The bow is likely to take more wave/collision loads.

If your goal is to improve performance, let's take a look at the payback. If your waterline length is 40' (guessing), your theoretical hull speed is 8.5 knots. Adding 4' will boost this to 8.9 knots. A lot of work and expense for 0.4 knots.

Then you have a boat which will be difficult to sell (= poor resale value).

My recommendation would be to either fit folding props (should get 0.5 knots more) or as someone else suggested, sell it and buy a more performance-oriented cat.

[captlloyd]

Originally Posted by Simi 60

Why didn't you follow the line?

I agree, the line is a bit off, but still a nice job. I wouldn’t think it would be that hard to correct it at this point. By the way, I think it would INCREASE the selling value. I like it.

[jmh2002]

Originally Posted by spiv

I totally agree with all your statements.

PS: by comparison I think Parlay Revival made their's too small, at about half the size of yours...

[catsketcher]

I find it interesting in this thread how there are lots of people writing how stern extensions don't work, when about 20-30% of the cats out cruising in Australia have had them fitted. They don't cost a heap and they usually make the boat a much better boat.

Catamaran naval architects know that designing a cat is strange because the hulls get lighter if to windward and more immersed if to leeward. So the idea that having a transom slightly out of the water being nonsensical is wrong. The leeward hull when depressed will have a more heavily immersed transom and unless the transom is capable of dealing with being more immersed it will increase drag more. Watch the leeward transom going to windward, there is lots of drag around there if heavily immersed. A clear transom is a great idea of the transom is big and fat, like a Lagoon.

Our cats also tend to get heavier in the bum rather than in the middle, with dinghy arches and the like, so adding better flow at the stern makes sense, it does not add a lot of volume really, but it does add a lot of pitch resistance. Out of all of the cats I know that have had stern extensions (about 5 off the top of my head), some make some speed improvement at low speed (I think due to transom immersion reduction), all improved speed at higher ranges (Not digging holes), all improved access and all increased pitch resistance, some greatly. All made the cats look better and every single owner said the extra length and money was well spent. Boats ranging from Crowther 10, x 2, Seawind 1000, Simpson 40, Fastback 30 (to 36ft!).

There is a fair bit of speculation about adding extensions from people who haven't done them. They are a cheap way of improving your boat. Here in Australia people do them for not much money and their boats are much better. It would be silly to buy another boat when all you want is to clean up the wake of the boat you love.

When my mum's C10 had a transom extension (1 metre) and a stripe added I didn't recognise the boat for a few seconds, she looked so much better. She was a bit of a pig and with the extensions and a new main she was a brand new boat - a totally different beast from before, much faster, less pitchy and finally good to look at. So the people who think that extensions don't make a diff haven't seen the smiles on the dials of the owners who see the boat they love go from a pig to a swan. Cheap at twice the price.

[smj]

Catsketcher you are absolutely right. Having owned a Seawind 1000 then later adding 4’ to the stern the advantages were obvious. A much cleaner wake, faster speeds, but most importantly a HUGE difference in the motion. Made that 33’ cat feel like a 45’er. Now every time I see a non extended Seawind 1000 I wonder why and I wonder if the owners know what kind of cat they could have with a small investment.

[malbert73]

I’m a non cat owner but own a monohull that is exceptional (for a loaded up cruiser) in light and moderate air and is whisper quiet in these conditions with no transom drag. I’ve always wondered why many cats I’ve seen/sailed on drag transoms through the water. Immersed transoms only help with planing/surfing….

So stern extensions that clear the waterline should also add light air speed I imagine. When/if I shop for a cat, well done stern extensions would add value in my eyes

[catsketcher]

For those wondering how a small change in transom immersion could change light wind speeds with a transom extension remember your dinghy sailing days. If you sat too far back in the boat (in light winds it is very easy) then you would not have a clear wake and you would go slowly, often very slowly. Sitting forward lifts the transom out of the water and the wake streams cleanly out from behind and is much much faster.

With some designs (like the Tasar) there is a reduction in wetted surface from moving forward but with other designs (such as modern 16ft skiffs) there is little change in wetted surface from moving but an immersed transom is still deadly to speed in light winds. The crew often sit/stand on the foredeck to get the wake clean.

When Lock Crowther brought out John West back in 1988, people thought he had lost the plot because the transoms were immersed at rest. What Lock told the doubters was that this was a race boat and its (rather narrow) transoms were designed for a minimum speed of about 6 knots and she was aimed at 10-12 and above. So the upsweep or release angle was made shallow. I remember looking at the Irens 40 trimarans from 1992 and being amazed at how heavily their transoms were immersed, but they were trimaran bums and they only get lighter as the wind picks up. Also again, they were designed for a range of speeds starting well above cruising speeds.

Racing boats, like a planing powerboat or dinghy, will have straight/er lines aft and immersed transoms. Boats that have to work well at lower speeds, will have transoms that are only slightly immersed (if the transom is narrow) or clear if they are to sail well in light winds.

And isn't that what cruising is about? Most cruisers don't want high top speeds but do want a boat that pitches less and performs better in light/moderate winds in waves. A clean bum and extra pitch resistance will help there.

[jmh2002]

All good stuff @catsketcher