new but ambitious

Missinginaction:
OK, maybe I'm seriously underestimating certain costs here, but since they will be spread out over many months, I don't think it's gonna be a very big problem.
As said, I live in Thailand, where climate is warm all year round, so it'll only need protection during rainy season for rain and air-humidity, but by that time all the timber should already have been treated for humidity, so I don't expect that to be a real problem if I can keep it out of the rain (please tell me if I'm wrong here!).
Also, i want to make the boat trailerable, thus avoiding most of the storage costs once it's ready.
Keep in mind that for many things, Thailand is a lot cheaper than the US or Europe!

Par:
thanks for the insights, I certainly take them seriously!
I'm not an engineer, but my father was (and a teacher) and I've learned a lot from him when it comes to "constructing things" (no boats sadly, but certain principles are always valid).
I had several years of technical education, where I learned to make technical drawings and calculations>
To answer your math-question: I am very comfortable with basic algebra and usually do most calculations off by heart, unless they're 3+ digits after the comma.
As I said before, I am seeking assistance (and already found it!) from a real naval architect to check my ideas, calculations and designs, so I'm not taking any stupid risks here. I may be ambitious, but I'm not a complete fool!
As for your other remarks, I have no experience with substances such as epoxy and haven't had the time yet to study their properties and calculating their use on that base.
As I understand it at the moment, how much you'll use mostly depends on how strong you want the hull to be (which stress factors are expected).
By asking that question, I was simply trying to save myself some time by trying to get a direct answer from someone with experience.
I have already studied several study-plans and am completely basing my design on what I've seen here (just longer!).
As for your remark on "my design not floating upright on the day of launch": I do have the feeling you take me for a complete idiot here and you haven't read (or choose to ignore) everything I've written before.
I've already done some research with regard to boat-balance and I believe I understand/know the most important aspects of it by now (not everything off course, but I'm still learning!).
To conclude, I'd just like to say (repeat) this:
I'm taking at least 1 year to learn as much as possible about building and designing a boat (the most important aspects, such as balance calculations, hull strength, safety) before starting the construction, AND I'm not doing everything by myself, since I will have all my calculations and designs checked by a real naval architect!
Hopefully this clears things up about my sanity!

 

For the record, I'm only talking about plywood boat-building and planing hulls here!
I'm not researching any other design form, since I won't be using them.

 

Re-inventing the wheel is seldom fruitful, imo. It is a big enough job to build a boat this size from detailed plans, that is a proven design, than to start a large scale experiment that more than likely will disappoint. And even if it does succeed to your satisfaction, will not be readily saleable, because it is an "orphan". If you say there is no intention to sell, that can change as life circumstances change.

 

I understand your reasoning Mr Efficiency, but doesn't the satisfaction of "creating something special" count for something?
Personally, I like challenges like this, not only for the satisfaction of creating, but because it forces me to learn new and interesting things!
As you already suspect, I don't really have the intention to sell it, but this could indeed change in the future, who knows.
However, if the quality of the work is good and the price not excessive (let's say construction costs + 50%), I don't think it will be very difficult to sell, since it will still be a hell of a lot cheaper than buying a similar boat new from an official dealer (200.000$ instead of 30.000???).

 

For most of us normal humans, it takes several years of study in various disciplines. Even as a full time student, you'll need a few years to get a grip on the engineering and hydrodynamic portions of a project like this. Seems a long way around the bush, for a one off to me.

 

Pipergsm, I can only suggest you post a rough drawing of what you are contemplating, so others can give an appraisal of it. I don't know what the price of diesel is in Thailand, but what you have in mind won't be cheap to run by any means, so whatever you save initially will soon be swallowed up by a hefty fuel bill, especially if your design is not as efficient as it might have been with a proven hull.

 

OK, maybe I should not use the word "designing"here.
What I'm doing is this:
I took a lang and good look at some study plans for plywood boats (up to 25'), seriously studying how the hull is being constructed (planing hull) and why it's done that way.
Next, I draw exactly the same kind of hull, only longer and wider.
Knowing the length/beam ratio for good balance and being able to calculate the CB and the correct weight distribution inside the hull for maintaining good balance (yes, I do know these things!), I should now be able to create a hull that is "safe" from a balance point of view, and has the dimensions I desire.
I can also calculate the approximate weight of the entire boat (once finished), so all I need now, is to ask advice from a real designer/naval architect with regard to the dimensions of keelson, bottom and side-battens,etc....., required in order to create a hull that is strong enough to withstand the stress factors it will have to endure (regarding desired speed etc.). These are things I'm not able to calculate, so I'll just ask the advice of a professional for this.
I also know the formula's to calculate the necessary HP for this particular design, needed to obtain the desired speed (theoretical speed off course).
Based on all this information, I will finish the technical drawings, before finally asking the real designer/naval architect to check my "designs" for serious flaws and correct them if really necessary from a safety point of view (I'll pay for this off course!).
Will this boat be perfect? No!
Will it be safe and fun to use? Yes! And that's all I need!
Does this mean I'm a boat designer? Off course not!!!
But I didn't need to be one to make this boat.

 

Mr. Efficiency
good idea. It'll take some time because I'm on tour now (being a tour guide) and I'm getting married soon, but as soon as I'm home and have some time, I'll do that.

Off course it won't be cheap using this boat, but I'll only use it to visit nearby islands (about 200-300 km), spending a few nights on the boat at roughly the same area (enjoy the beach, snorkeling and scuba with the family), and get back to the mainland, a few times a year, so basically, the boat will probably travel no more than about 3000 km/year!

 

The main criteria for you should be safety and comfort, especially with the wife and family involved, many women simply will not tolerate scary or uncomfortable boats, and if you are contemplating traversing open, unprotected waters at speed, it is a tough essay to fill that requirement on a lowish budget. If your radius of operation is less than 30-40 miles, and an hour or three longer in transit is not an issue,a slow displacement boat may be a better option. The motion is friendlier, and the running costs a lot lower.

 

"nearby" 200-300 km ? can you refuel at these islands ? If not, a planing boat is really going to struggle with range.

 

Mr. Efficiency,
A displacement hull will indeed be economically more interesting, but traveling at 10 knots doesn't really appeal to me!
Correct me if I'm wrong, but imo, the way you design the hull (for stability and relative speed) has little to do with budget.
As I said, I'm not a speed maniac, so if I can travel at a cruising speed around 20 knots (or a little more), I'll be happy! Doesn't have to be the really high speed.
But even for 20 knots, I'll need a planing hull if the boat is only 39' long.
I don't know about the re-fueling possibilities at the islands, but according to the information I found so far, a diesel uses about 1 gallon/20HP it produces.
If all my calculations are correct, my boat will need max. 200 HP (10 gallons/hour) to reach about 22 knots.
Travelling 300 km (go and come back) will thus use about 75 gallons (less than 300 liter).
Although I just discovered a flaw in an earlier calculation, a 100 gallon tank doesn't seem exaggerated, and I can always take a few extra containers along to be on the safe side.
I must admit however, I will be seriously limited whenever I want to go a little further, so I'll have to think that over.
Please keep on sending me your ideas/comments!
It forces me to think things over again and make the necessary changes!

 

How is it possible you can:

Yet, need this information:

Simply put, if you haven't a clue about the scantlings, how can you do a weight estimate, let alone have any idea about CB, CG or any other areas of trim or balance.

I can tell you, professionals get this type of request regularly and the resounding reply, is they don't want to touch the job. This is because regardless of whatever your "calculations" might be, the professional has no choice but to treat it as a full up custom design, running all the calculations themselves, if for no other reason, than to insure things are where they need to be. At this point it's no longer "your" design but a wholly new one (reconciled?) created by the NA or designer with styling and general dimensions loosely based on your input.

Again, you should post some sketches and more importantly call a few NA's and find out the costs associated with your "avenue of pursuit" in this regard.

 

I don't follow how you arrived at 39 feet as the desired length, but if you have the perception of travelling at 20 knots with comfort on the open sea in a boat that size, your estimates of weight, installed power, and fuel consumption seem well short of reality.

 

PAR and Mr. Efficiency
I realize that my knowledge in this matter is infinitely more limited than yours, PAR, and that my reasoning may seem ridiculous in your eyes.
However, according to the information I found so far (please correct me if this is wrong!):
CB is calculated on the volume of the hull, not on it's weight.
weight comes into place when you start calculating the total weight distribution of all the boat-parts, in order to get a proper balance.
Beam-Length ratio for good balance is usually 1/3, but decreasing as the length increases.
According to the hull design software "Freeship", for 12 meters length, beam should be 3.7 meters (or more) to have good balance.
I do have some idea about the required dimensions for minimal hull-strength, and will base the preliminary weight calculations on the dimensions I believe are required to obtain that minimal hull strength. These calculations may or may not need correction.
Please keep in mind: what I need is safety, not perfection!
When it comes to the required dimensions for deck, cabin etc., I'm pretty sure my calculations will be rather correct, and thus will be the weight estimations.
This should result in my total weight estimations not being too far off.
I believe (Hope!) I can keep the total weight around 3.000 kg.
I found this formula for speed calculation:
Vmax. = k x root square of SHP/LT (HP at shaft/total weight in long tons)
For this specific hull design (planing, hard chine, +30' waterline), the K-factor should be about 3.2 or more (theoretically)
So, if I have a 300 HP engine, this will be 3.2(K) x 10 (root square of 300/3) = 32 knots max. speed.
Reducing this with more or less 20% should obtain a fair cruising speed (25.6 knots).

Again, I base this on information I found on the internet, from sources I believe are reliable.
Please let me know if this information is not correct!

I have already contacted a NA, but he's waiting for my drawings/calculations (could take a while), before deciding anything with regard to remuneration.
Maybe I'm being naive when it comes to the help I hope receiving from a professional (as you seem to think), but even if certain values have to be recalculated and re-design is necessary (I believe changes will be limited), in my mind it will still be my design, realized with the help of a professional!

 

Mr. Efficiency
it doesn't have to be 12 meter (39'), 12 just seemed a nice round number and coincidentally provides a nice long waterline to improve speed potential!