economical coastal cruiser

got it thanks Rick.

i'll end up like most people - buy/build the longest boat i can afford! BUT Not park it in a marina, use it and have it on a swing mooring in the river for 'dirt under the feet periods'.

My budget is going to be largely governed by what i clear from a house in Melbourne that is 'surplus to current requirements' but tenanted until later in the year.

Guys i appreciate your constructive suggestions and willingness to help. But as i'm a few months off key decision criteria (budget being one) i don't want to trouble any of you further just now with details that take time to put forward but wont be acted on immediately.

 

I am surprised

What is the price tag of the intended boat ?

It will be the first question any salesman will ask you if you are on the buying market.

I have not found it in the 12 pages of this thread. It has to be answered to check if it is a real request, not like I want an cheap luxury item.

 

Rick,
I think 2 tons could be too light, at least for what I guess is the weight penalty of my own comfort requirements (or wish-list). It would be interesting to see the power vs. length graphs for 3 tons and 4 tons as well. Actually I think 3 tons is the limit to what I could handle on my own, when aproaching a jetty in waves and wind.

Reagarding size, the central hull also needs to be wide enough for an engine installation, and wide enough to stand in when standing height is needed in the forward cabin. In my opinion this means that the width should be more than 0.8m.

Active roll stabilisation with servo-controlled foils as suggested earlier in the thread shouldn't be ruled out, although for me it's an undesired complication. Everything considered it might turn out to be the best solution after all.

Erik

 

I have attached for 3t.

You can see the trade-off. Unless there is some other major objective like Marina costs somewhere around 16m will be getting close to the optimum for this displacement.

If you are happy with this we can move on to stability constraint.

Rick W

 

Issues restraining boat length in Sweden

Thank you Rick,
My conclusion is that 3 ton displacement still should meet the 12/12 requirement if the length isn't too severely constrained.

I've checked some issues that have bearing on boat length in Sweden. They may not apply to other countries.

1) License. With the present laws, no licenses or permits are required as long as the boat isn't longer than 12m and wider than 4m. For once, formal logic applies to laws. "And" really means "and", so length doesn't matter as long the width is less than 4m. Speed doesn't matter either. Unfortunately the law is expected to change soon, so a license will be needed if the boat is longer than 10m or faster than 15kn. Larger than 12m*4m will require a tougher license, as will speeds faster than 30kn.
Most owners of the type of coastal cruiser discussed in this thread can be expected to go for a license anyway, in order to be able to drive boats faster than 15kn. Restraining the length to be <10m will therefore not be important. I don't expect such a license to be a big deal, but I'd rather minimize my dealings with authorities.
Width should be kept <4m to allow the length to go beyond 12m without the need for a tougher license.

2) Harbour fees. At several popular guest harbours there is a fixed standard fee, in my opinion quite low, for any boat shorter than 12m. Longer boats get charged more.

3) Marina fees. The tradition in Sweden is to lay the boats with the stem towards the jetty. Width is cost driving, not length. Where I have my boat we're charged per meter jetty we need.

4) Trailer requirements. The total length for towing car plus trailer must not exceed 18m. I used to be 24m, but harmonization within EU has forced us to put the limit at 18m to not distort competition within EU. The 18m requirement leaves something like 12m for the boat.
The width restrictions for a trailer are similar to most other nations, and probably identical within EU. Of course it's no major problem to get an exception for any width that is physically possible to tow the desired route, but the practical arrangements are awkward. In reality <2.5m is preferred but up to 3m is OK.

To summarize it: Length should be <12m and width <3m (or rather <2.5m) to keep cost down.

Erik

 

Eric
interesting to read the issues you noted. Licencing in Australia isn't that problematic yet, but i've no doubt we'll end up heading that way and so i take your comments as forewarning!

trailers are pretty similar, but vary in detail from one State to the next at present which can be frustrating. Typical and likely to be uniform soon is width 2.5m max, height max 4.3m and trailer length max 12.5m. Likewise, exceptions are possible (but very different from State to State) and up to 3m not too onerous although 'daylight hours only' typically applies.

although i'm aiming for a 'mini-Dashew' in the medium term, i've had a reality check and will go with Sandy's original concept 'barely trailerable' for a 'test' period. I've been almost exclusively been 'day-boat' in the past with things such as a 28 ft cat with 2 x 200HP outboards. I no longer need to do 40k to rush home for work or kids school, and am no longer inclined to 'feed' that many horses which inevitably get used if they are there. My 'test' is to confirm happy for days on end on the water, which would be weeks and maybe months at a time if in due course i go with something like Pierre briefly spec'd a few posts ago.

I agree with your summary of dimensions and as someone posted, the competition that is soon closing

http://www.woodenboat.com/wbmag/designchallenge2.php

should deliver some possibilities. A pity that they specified just 1555kg (assume dry boat, with allowance for trailer, fuel/water and essential junk as extra). Another 1000kg in the boat would still be trailerable. Our weight rules have a number of categories, but large cars/SUV can tow a suitable trailer with all up weight of 3500kg. Some SUV can go to 4500kg, with higher spec coupling etc. Of course for any distances a pickup truck or motorhome as tow vehicle will be give a better comfort/safety margin. If i get serious about visiting lots of distant places then an 'old' trayback 4WD with Fifth Wheel coupling will likely be the answer. I'll be nervous about leaving an expensive SUV in a public parking area for too many nights!

i'm hoping one of 'our' professional forum designers tweak their ideas to fit the challenge criteria, but then as a 'possible option' provides a heavier solution also as i fear the weight limit is going to mean much less than 12m length. The $1000 prize is minimal but the kudos are priceless aren't they?

 

ERik
We can move foreward with this as a first pass. 3t, 12m, 12kts, 2,5m. The length and beam seem to be hard constraints important to you oblective. It is unlikely the optimum solution will be less than 12m. There is still some possibility of coming in under 3t.

The next most significant factor from a powering point of view is stability. I have analysed quite a few options and can offer the following comments.

1. Satbility is a function of the second moment of area of the waterplane.

2. The best initial stability will be achieved with a catamaran form with slender hulls set to the maximum width. The cat will have high power requirement than a mono if the length is not heavily constrained. Anything that is limited to 2.5m wide could probably be made self-righting.

3. You can achieve reasonable initial stability with a monohull. It should not be difficult to achieve self-righting.

4. There can be combinations of form stability and ballast that give a superior overall result. I have previously determined for a lower speed case that placing the smallest ballast weight as deep as possible is the most efficient from a powering perspective. Obviously it creates issues for draft and trailering.

5. A stabilised slender monohull is the most power efficient method. The boat does not snap roll as much as a cat and there is no extra power needed for calm water operation over the lowest drag length constrained hull.

I expect the optimum method of achieving the required stability will be either based on 4 or 5. For operation in the southern ocean I would likely favour 4. That said the Ady Gil (Earthrace) operated successfully in the southern ocean. Note though that its beam was considerably greater than 2.5m and it is unlikely to be self-righting.

The attached shows the power and beam for the lowest drag hulls having the respective stability constraint. A beam limit of 2.5m beam will give a KMT of 2.8m, which I expect will be more than adequate as the detail unfolds. At this beam the power required is 12.4kW.

The stabilised monohull requires 8.3kW and can achieve the same initial stability with tolerably large stabilisers.

It is clear that the stabilised monohull has a distinct advantage here. Unless you have particular reservations about the concept I believe it will result in the optimum vessel. The concept is now finding growing use. Here is a good example:
http://www.marinelog.com/DOCS/NEWSMMIX/2009jul00291.html

I have tested this concept extensively at my pedal boat scale and find it to be the best of all ideas so far. I can understand why it is growing in popularity.

Rick W

 

Rick I notice there is never any mention or asking what a person might want inside one of your hulls. How do you do an optimum design without knowing what a person wants? Are you just assuming that you will put the stuff where ever you can and what weight to much just leave out? Is a constraint the same as a compromize or is it a optimization word?

 

How about building something similar to these, in steel, aluminium or wood \ plywood epoxy?

http://www.georgebuehler.com/Wunderberg.html
http://www.georgebuehler.com/ellemaid.html

 

There's lot's going on in this thread...appears to be several different boats are being discussed now.....

One set of specs was mentioned for a mini Windhorse or a "low-cash" FPB64. The sketch below is my take, a scaled TimberCoast 22 hull. Full displacement, vee-bottom, plywood, foam/glass, or aluminum sheet material construction. Essentially a direct descendant of LFH's Marco Polo.

I don't really think a 55' boat makes much sense as a coastal cruiser, something about 38' would be a lot handier if one is in and out of harbours, not to mention moorage fees.

 

Rick,
I really appreciate the effort you are putting into this, and have absolutely no reservations about the stabilized monohull. To the contrary, I’m interested to see how far this concept will carry, hopefully all the way.
An iterative design process has to start somewhere, and an assumption on size and type of hull is in my opinion not a wrong start. We’ll find out what kind of boat we can make out of it. I’m reasonably positive a weight budget summing up to 3 tons will allow the comfort I need for cruising the Baltic in summertime, but there is no way to know that until we have an idea of what the weight of the basic empty boat will be. I’m also a little concerned that the physical shape makes the available volumes in the boat difficult to use. I guess we'll get an answer to that later on.
Erik

 

You are impatient.

We are close to establishing the footprint to work within. I am certain the client has some reasonably firm requirements for his layout within that footprint. The designer's objective is to take those requirements and optimise the use of the available space to match the requirements.

It is cart before the horse to present a layout that may not fit within the footprint or make assumptions about what the requirements might be rather than what they actually are.

Rick W

 

Rick if your client will give on 12 knots and 12 nmph to get more stuff then you have not established anything. You have wasted your time and must start over to find the optimum hull for the stuff you customer wants.

Talk about impatient, you wanted to move to stability before you knew whether you client wanted air conditioning underway , a shower or even a queen size bed! You want to optimise a hull and then force the customer to fit inside, no?

 

Erik
There will be interplay between the available volume, stability, motions and ultimate safety. But for now we will go with the stabilised monohull and see where it leads.

In the first iteration I would like to get as quickly as I can to the power requirement as I entered this thread on the basis that it "may" not be worth the effort to consider an alternative to a standard outboard prop. I believe prop selection is an important element in economic cruising and should be optimised.

With a relatively easily driven hull windage becomes a big factor in determining power - with the stabilised monohull it could be considerably more than wave drag. Even in relatively protected water the wind is still present.

For the first pass we have a firm constraint on beam of 2.5m. So the height is yet to be fixed. I suggest 3m above water level for this first pass. So total frontal area will be 7.5sq.m.

You know your waterways better than I do so you need to advise the operating conditions that you would like to maintain design speed in. The attached chart shows what additional power will be required to push the 7.5sq.m superstructure through the water at 12kts into the nominated headwind.

The chart is based on a Cd of 0.3 on frontal area. It may be possible to get better than this and it should not be impossible to achieve 0.3. Point is the windage is a significant constraint and is going to be a consideration for the optimum solution.

For the waters I am familiar with I would work on 20kts in the first pass - means 5.2kW extra required to drive the boat. If you are in a windy location with short fetches then you may want to select higher than 20kts.

Are you happy with 20kts. Do you want higher? Are you prepared to accept reduced speed at 20kts and select something lower?

Rick W

 

Getting off topic at least partly my fault ....apologies to all. But a short word if I may:

Milan, Tad: Thanks for comments and suggestions. Tad i think you're right on 38'

But over to Erik and Rick, who are on topic.

On that one, could some of the height be achieved with a 'pop-top' like some caravans? No windage saving on the water but towing would be a lot better and as the W x L dimensions are close to fitting inside a shipping container, could the 'top-down' height be also trimmed likewise? Er, maybe that is another thread or merging with another thread also. Even if containerised shipping is not required, reduced height offers more undercover storage options.

Pierre, i'd agree with your approach if it was a non-trailerable design. And i'll be honest and concede that i will place 'comfort' into the mix early, like you advocate. But for a trailerable, i think getting the max. volume possible with sufficient stability is the best approach. The interior is somewhat compromised at the outset, and a minimalist approach to that might be best. For a couple of weeks on the water at a time, some of the interior of the pop-top caravan could work well (suggest omit the aircon ). Before someone tells me to just put pontoons under said caravan when at the launching ramp, i'll remember that we are talking 'coastal' and not 'smooth water'.

The pop-top could be for the salon/fwd section only, and have zip open clears etc for ventilation or weather protection. It would be raised at anchor and lowered & fastened when underway.