Placement of chines in multi-chines

There is a big difference between aircraft and boats. The shape of the hull above the waterline has a lot less resistance than the submerged part. That is why the upper chine is usually a cosmetic detail. A chine can lower resistance by deflecting the flow away from the hull surface above it. High speed boat have steps and lifting strakes to accomplish this. The why does define the where. Once you decide what you want the chine to accomplish, it will determine the position and shape. Also, the overall shape of the hull will change depending on how many chines there are and where they are located. There is no universal answer to it. Placement of chines also changes the flare of the panel, which then influences the behavior of the boat. For example, a lot of flare will produce a lot of reserve flotation. If it is too extreme, the boat will have an uncomfortable motion but more dynamic stability. What do you mean by "small boat". If it is a dinghy size like I am understanding, the speeds you propose put it into the planing mode, not displacement.

 

"There is a big difference between aircraft and boats."
Now I understand everything.
After all this explanation, I think I'll leave the thread. Makobuilders, good luck.

 

Another Gonzo/TANSL sideshow ? The OP is just trying to get the best approximation of a round bilge displacement hull, without compound curvature.

 

Again, as I mentioned as apparently the OP has done previously, some testing helps a lot, if you need specifics, though some general guidelines can be followed, depending on SOR priorities.

Yes, aesthetic can play a huge role in the exposed chines, particular areas at the bow and stern. I designed a 20' performance sailor recently, round bilge, square top, etc. and though her performance envelop suggested she could use a chine aft for flow separation, I could bring myself to put one on, because it just detracted too much from the sweet lines of the round bilge form.

If you take a look at a single chine hull form, the seemingly logical location for a second panel might be to bisect the single chine, making the garboard or bottom panel(s) smaller and decreasing wetted surface. Unfortunately, this usually requires the single chine line to flatten a bit, particularly at the bow, otherwise the bisection of the typical single chine, distorts the bow sections quite a bit.

These considerations can be very different if the hull form is strictly displacement, compaired to say high speed. Knocking down spray can be vital on a full plane boat, yet a minor consideration on a full displacement yacht.

In an ideal world, you'd like to place the chines to best mimic a round bilge, with the attributes you desire, but developability often forces your hand. Additionally, having to move volume around to suit requirements, may force less than desirable chine lines.

 

It could be interpreted as that but I considered two things:

• A "chine" as I understand this concept, has a reason to be to solve or avoid a problem and therefore has nothing to do with aesthetics. For me, a decorative element can not be regarded as "chine". Say it is a decorative element can lead the OP to take wrong decisions.
• If what the OP wants, for whatever reason, is to imitate a curved bilge by straight sections, hydrodynamic considerations, increased resistance, water lines, etc., has littel to do with it, could be better a constructions issue. So my post # 15 asking what was the type of "chine" we were talking about.

All that, in my opinion, has nothing to do with my friendship with Gonzo. I tell you, honestly, to have an opinion contrary to Gonzo does not mean I want to attack him. Just I try to prevent the OP does something wrong thinking that some aspects of ship design are not important.
If I am wrong, I am available to accept all the criticism that you want to make my reasoning. I do not take that as personal attacks, phobias, ....

Makobuilders, I'm so sorry, my intention was to get real help for you.

 

Not #1 in your post #15, TANSL. He is concerned about eddies caused by submerged chines.

 

Yes, I know that. Thanks. After reading several answers I did not know what we were talking about.

 

Chine locations certainly can be altered for aesthetic considerations and often are on yachts, though with working and commercial craft much less so.

 

I do not doubt, but it does not seem a good practice. The shape of the chine substantially affect the ship's hull, which should not be defined, although I know it is done, for aesthetic reasons.
I would never say that the situation of the chines is an aesthetic issue. Unlike, it is a very technical matter that, for reasons of aesthetics, could be changed slightly.
But this is just my opinion.

 

Round- multi-chine- or trapeze-bottom

I have designed many boats with multi-chine the last fifty years. The difference between a round-bottomed boat and a multi-chines boat is so small that it can not be measured in practice. There are other details that can make very much greater difference. This of course assumes that the chines have been placed with the utmost care.

It has also been found in practice that a multi-chine boat can be faster in the higher speed range. It should also be noted here that no chine is for aesthetic reasons. All the chines has an important function. The worst option is a boat with only one chine, V-bottom.

Right now are two equivalent rowboats tested , one with round bottom and one with trapezoidal bottom.

js

 

Almost all high speed powerboats have a single chine. Why do you think it is the worst option?

 

We're talking, I think, about multi chine, not planning hulls, boats.

 

Boats of any design type may plane, regardless of the amount, or lack of, chines.

 

That's a very strong statement. I would like to see an aircraft carrier in planing position.

 

Singel chine or multi-chine

According to my calculations, measurements and practical experience, it turns out that a trapezoidal bottom or double-chine bottom is superior to everything else. Depending on what measurement we put as the norm, V-bottom have lower stability, greater wetted surface, higher wave drag and/or higher g-force.

js


https://www.youtube.com/watch?v=cXDfQqxJ_pM
http://sassdesign.net/U-botten rev 03062010.pdf