Stretching a hull

Hi Barry.

Aft of the weld by the blue support the hull is the same shape (save for keel).

If you look at the keel you'll see a patch (behind the jack). The patch is a result of a repair that was made on the wet side of the gland seal on the prop shaft. In front of the patch, circa 50 centimeters, is the transmission and then the engine. You can see two drains from the deck (one big and one small). The engine compartment extends approximately to the small one.

One fuel tank today, sitting under the cabin. I may be possible that a drive shaft will be able to fit below it but I'm counting on having to make two new ones (one on each side of the shaft).

The problem with my upgrade is that I need a bigger engine. But since the engine needs to be heavy duty and keel cooled I'm not only looking at bigger engine as in more hp but also volume which results in physical size and weight.
In combination with a bigger transmission, that needs to sit a bit higher than the current one to actually be able to fit, the new propulsion would be approximately 500 kg heavier than the current one and on top of that sit higher and more forward (higher and longer engine).
So all in all the cg (which is already to much forward in my opinion) will be even further towards the nose and the installation will rob me of even more space on the cargo deck than the current on (which already now is an issue).
Also, more power leads to more cooling. While possible it will be time consuming to increase the cooling tank area within the current hull (but circa 2 meters of extra hull will provide plenty of area for tanks).
In addition to this I would need to move/reconstruct the current bulkhead ahead of the engine compartment as the new engine won't fit in the current space available.
And I still wouldn't get the extra cabin length that I need (or at least would like to have).
Almost forgot, the current transom isn't well designed, the sharp corners makes it hard to reverse in ice so another benefit of making her longer is that I can fix this flaw in the design.
At last, a new shaft will be needed, as well as a larger prop to get full gain from the extra hp and torque, so much work will be done to the hull anyway.

 

Magnus
I had assumed that there already was a V drive in the boat because I had put a ruler on the propshaft line which if it was a straight drive, would have put the engine,
well, where it is. I don't every recall seeing a planing hull with an engine so far forward. Mid ship and stern locations being most common.
I see that most of the Capo new boats have engines in the back, Volvo duo stern drives, I suspect, which do not seem to give a long service life without intense maintenance. I am pretty
sure that my Volvo outdrives oil change interval was a 100 hours and many commercial operators in the pacific northwest keep complete rebuilt outdrives as part of their spare parts list for fast change outs.
One fellow that I know had 3 aluminum crewboats and he said he gets about 350 hours between rebuilds. I am not sure what model of the DPH that he had. They started at DPH-A
and are around revision DPH-E to solve the inherent gear and other problems.

Have you called them to discuss the stretch?

This seems like it is going to be an expensive project. I am sure that you have done the calculations and determined that selling this boat and buying a longer higher horsepower similar
boat would not be cheaper with less down time?

Good luck and keep the thread posted with the refit.

 

Petter Håkanson is the current designer of Capo Marin, he started his own business in 1998, but this doesn't exclude the small chance he was also involved with the design of Magnus' Capo, maybe he's open for a chat about the proposed mods . . ?



The Capo 145 looks like a nice boat for inspiration for Magnus' mods, but it's a jet boat . . .

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Next one is just to have the picture on this page too...

 

Between 100 and 200 hours between oil change on Volvo outdrives (depending on model) which is on par with others. One of my boats has an outdrive and what it gives excellent performance (speed, maneuverability) it takes back when talking about service and longevity. I get approximately 2000 hours between overhauls but then I pamper the outdrive and I don't run a supercharger (the instant torque increase that the booster creates at a fairly low rpm is a leg killer).

Yes, Håkansson might be a person to talk to. Good input. I suspect he may have had a hand in designing my boat, at least the bow is clearly current Capo-style.

I'm constantly checking the market but fairly speedy but yet sturdy and fully ice going boats are quite rare. And while this whole project will be far from cheap the cost of the stretch won't be too bad and I'll have to spring for a new propulsion anyway. (I'm planning a new build but that's another project that's at least two-three years from now and I need this boat operational in the meantime.)

 

Guess that's because you have to carry the weight penalty for the ice capacity for about 3½ seasons per year, while the actual ice use of the ice capabilities is about max 2 × ¼ = ½ season annually, this is assuming keeping about a ½ season mid winter thick ice down time anyway, so the gain of max 10 cm (4") solid ice capacity at the start and end of winter is about 2 × 3¼ = 6½ weeks of extra use annually . . ?

If this is ± correct, then vs. a similar non ice boat, is there enough financial gain in the extra initial investment in 10 cm (4") ice capacity, plus the year round higher running costs, and the carrying capacity constraints which the extra hull weight gives . . ?

 

The main penalty doesn't come from weight, it's not a very heavy boat albeit slightly heavier than a non ice going counterpart, but rather from a less effective prop and oversized power train leading to greater losses due to poorer efficiency.
In turn, this is in some part offset by lower maintenance costs in some aspects like no need for expensive impellers or having to winterize the boat or maybe even having to take it out of the water. Also, in the long run, I suspect I get more hours from say the engine because it runs almost every day and doesn't sit for months.

As for the season, every year is unique. The last few winters have been off-and-on so the ice has come and gone. The archipelago here is the second largest in the world and we're pretty far out so we have open water for much longer than what they normally have further inland towards Stockholm.

We have a few official contracts that although they're not specifying that we need ice capability it's kinda implied. In our area we're just about the only operator with a true ice capable boat (but sure there are bigger ice going ferries) and thus we can provide a good service between when the normal boats stay at the dock and the hovercrafts take over.

A far as economy goes we'd probably be better off just closing down when it comes to that. But knowing that we have a boat that's capable of "everything" is quite nice and it helps you sleep. Like tonight for instance when temperature has dropped from 0 to about -8 (centigrade) and I know that I'll be facing some ice in the morning. But how much? It doesn't matter because there's no way things can get bad enough during one night so I know that I'll be able to fulfill my contract tomorrow.

And another thing. Crushing ice is fun. And very addictive

 

Thanks for the info Magnus, it's really interesting to hear how things actually work up there . .

 

Could you take a photo from the top? Seeing the deck shape would help a lot.

 

Photo from the top, then I need to find a big tree

Some pictures of the cargo deck and the current engine installation.

 

Totally off topic but here's a few pics of todays hard work. A small video here Wallner Marin https://www.facebook.com/wallnermarin/videos/1824899290865691/ and sorry if inappropriate to link to company fb-page.

 

I see a boat, so not completely off topic. It looks like the weather we have here.

 

It's quite typical for the kind of winter weather this boat's facing (although still and sunny today which is surely not always the case). Ice that comes and goes, sometimes open water, sometimes pack ice and never knowing from one day, or even turn, to another what you might run into.

 

Or a friend with a drone

Cheers,

Earl

 

Or park the boat under a bridge along the route, and go up there to take some top pictures, saw this bridge at a about 9.2 NM sail SW of your home berth, maybe you even know the red boat ?

 

Some progress and good news. After quite a bit of research I managed to find the designer of the boat, it was like following a trail of breadcrumbs. His name is Stig Hellstrand and currently living in Finland.

Anyway, I told him about my ideas and how I feel that the boat is performing as it is. He was interested in what I had to say and upon first glance thought that it was as a reasonable idea. He still has the original plans (which he'll send to me) and offered to crunch some numbers.

The only thing solid that he said right away was that I must take great care not to get the boat too buoyant in the stern vs the lcg. It rimes with my own analysis of one of the current problems and something I already wanted to deal with was part of the extension. I bit surprisingly though that he said it straight away, I can only assume that he's aware of the issue with the low buoyancy of the nose.