Comfy ride @ 25 knots?

My query probably covers stability, hydrodynamics and propulsion so I thought to post in design forum. Bit longwinded read ahead but it seems this forum asks for "why you wanna do this" a lot

Hi fellas, my only boating experience has been with mono hull planing fishing boats and inflatables in the 3 to 6 metre sizes so I need some help in understanding displacement types and multi hulls. I have been reading page after page of boatdesign.net am still a bit confused on some issues

Why I am interested in a comfy ride going 25 knots some may ask? Mr Efficiency??

My own last boat was a Mac360 from NZ to which I installed a low centre console, seat and 25hp 2st Yammie. The top speed on GPS at best would nudge 25 knots. For its 3.6m size, its a heavy 120kg PE boat and it actually was very comfy in the driving position in through some really bad chop in Sydneys Broken Bay, Botany Bay and Pittwater areas. Also handled wake from larger craft in Sydney harbour with lotsa grace as well as the swell just outside the harbors and bays. So thats the positive side of my experience with the planing boats

The negative, every time I go fishing with a Local charter here in Fiji in 26' glass or ply panga types launches. Or back in Sydney in other folks aluminum or glass boats. Feels like my spine is getting smashed. Even in things like 6m Haines and signatures


I am currently assembling my 3yr plan of starting a fishing charter biz here in Fiji. After 3 years of setup I hope to be taking 2 anglers per trip for standing up casting plugs to 200g with 8' rods running 100lb+ spectra lines. Currently I am working on building up the accommodation side of things as well as getting to know the fishing area, under an agricultural lease type of thing but in 3yrs time will change that to a tourist lease once the infrastructure is in place

Its time for me to think boats, there are some benefits to sorting that now under the current scheme. Either build or buy. Why 25 knots? Its a speed I know that is decent enough to get the range to the reef break in around 30 mins or less without being overly fast and placing clients at risk or even gear at risk. So that's the open throttle types speed I am keen on. Now every time I head out here in the mornings the weather is awesome but as the day passes the chop picks up to the point that by 2pm or so its a shocking ride back in, just continuous misery to be the passenger

What I am keen on is exploring the possibility of a 6m types boat that is more forgiving. Something that doesnt have a huge draft but doesn't pound in chop. Something that I can possibly build myself either from a kit or even make the plan myself after some learning and experience. Either from glass/ply or aluminum

Would I be correct in looking at displacements types 6m boat? Something that will move through the chop instead of over it? I don't really understand this these types of boats. The other important thing is stability for stand up and powercasting while waving some heavy and dangerous bits of gear as well as standing up and fighting with drag tightened to 15kg or more. So gunnels mid thigh height to groin and forgiving platform in the swell 30-100m outside the reef break

Please help with some directions on the type of hull I should be looking at? plans out there? Power requirements? The kind of draft i would be looking at for a craft that handles so? Above the waterline, pretty regular sportsfisher simple walkaround type boat with even sole fore to back and self bailing

Thanks for any thought on this

 

Looking at Groper's build here http://www.boatdesign.net/forums/bo...displacement-powercat-build-thread-38588.html

Maybe by hopes of 25 knots might be too optimistic, the 17 knots he is hoping for would still be plenty fine

 

Here is a fully submerged hydrofoil powerboat. It should be comfy at 25 knots.

http://www.foiltwister.se/index.php/en/

The price might be a bit high. Maybe they would sell the foils as a kit.

 

A 6 metre fishing boat that is going to handle the afternoon wind chop at 25 knots comfortably, and be a good stable fishing platform, is quite attainable. But it depends on how much you want to pay, and particularly how much ongoing cost you are prepared for. A good planing cat fits the bill. The old Shark Cat 560 was a great vessel on the water, small enough to trailer manageably, but they are getting long in the tooth now, they were heavy, hard on outboards due to mist and spray swirling around, and the rising price of fuel and costs associated with twin engines hurt too. But a fool-proof and very forgiving boat, like nothing else that size. A genuine 25 knot cruise in any conditions you would be able to fish in. I wish I kept mine !

 

One more thing about the hydrofoil... they claim fuel consumption is "reduced to about 25%." I assume that would be relative to an equivalent conventional planing boat. If that figure is at all accurate I would think that would quite an attractive feature for a working boat.

 

Looks awesome but I think something like that would be well beyond my scope. I dont have much to choose from locally in form of ready built new or used and anything available is too much on the pricy side as most had to be brought in from os I think I am looking for something very tame too

 

Mr E the Sharky looks good. Is it smooth running across chop in something like that? Will something similar in displacement mode offer better mileage and equal if not better handling to 20 knots or close?

Are there any plans around for boats like that? I am looking at sourcing a decent welding plant and learning how to work plate alloy so if somethng like that worth making in plate?

 

This been a good read, still trying to understand it all
http://www.boatdesign.net/forums/boat-design/efficient-10m-displacement-powercat-44519.html

 

You won't get any kind of worthwhile result from a 6 metre displacement cat, imo. Groper's boat is about the size they start to work well. And yes, the old Sharky rarely landed hard or hurt the body in chop. But the mpg figures are not that good, you could get 4 mpg from modern engines.

 

Been looking around online, there doesnt seem to be much in the way of a cat like the sharky available in plan or kit form

This from Glen-L looks alright though
http://www.boatdesigns.com/22-Wildcat-E-X-T-Sport-power-catamaran/products/903/
They make statements about rough water ride and stability. I am going to try to google up more info on it like build threads and such. Doe anyone know if there is an aluminum supplier in Australia that can cut from Glen-L plans?

 

They also list 20 odd knots at the lower end of the power option, do they mean with twin 90s?

 

Size will depend a lot on the type of fishing, what your customers expect, and how much deck space per fisherman is needed space for each style of fishing.

Trolling requires seating under shade and not much deck space.
Live bait fishing on the drift requires livewell capacities
Jigging and popping requires a lot of open CC rail length
Flycasters like forward elevated decks
reef and flats fishermen lke polling platforms
Big or small fish will detrmine storage and ice requirements.

But on the surface I wouldnt consider anything smaller than 22 feet, and that would have to be a cat to get a decent ride so that you can actually go out when the weather is not perfect which is usually the case with reservations made in advanced.

I think I would look at a used center console like Seacat 22. 2005's with twin 115 hp 4 strokes go for around 28K USD with electronics, ttop and trailer. They will get about 2.5 mpg at 25 knots with 4 aboard, which is the maximum load on this hull if you want to sit under the shade and still have room to fish, and this package will last you for years of daily service.

If you want a monohull, then 27 feet would be as small as I would go for charter service.

 

I think it depends on how many $ you are prepeared to throw at it, as to what you can do, realistically.

 

To get 20 knots at displacement, you need a long hull. I would think around 29 feet in a slim hull off the top of my head. My 22 Seacat does 40 knots, on plane, and it a dry ride that crushes chop.

The seacat has sponsons with flat bottoms and rounded sides that plane with extra power after displacement speeds have been passed. Salesman call it a semi displacement, which to me is like being a little bit pregnant, but thats its marketing term.

The amount you want to charge, distances traveled, and load wt also have to be considered, but generally 25-27 is considered a small offshore mono and 22 is a small offshore cats. Charter clients generally ask for larger boats with more comfort, and if you are going to operate 200+ days a year, you will be pretty tired of bouncing around in anything smaller. Do you come back to port in a following or head sea, for instance.

Let us know a little bit more about your competitors equipment, services, rates and what you plan to invest so that we can give you better advice.
But buying used will get you the boat, electronics, ttop and trailer free for the cost of new twin engines, and 4 stroke outboards will run routinely over 4000 hrs with reg maintenance. I bought mine with 500 hrs, so Ill take my dirt nap before they need to be replaced. Building a hull is a lot more time consuming and expensive, from a business point of view.

 

First thing to do is be acquainted with the local laws governing charter vessels. Boat may need to be built and equipped to strict standards. The skipper may need to have added qualifications.