few questions about rake of a boat??

I wasn't sure what forum to post this in. The few questions I have and I hope i can explain this so everyone can understand.
I've been wanting to build an aluminum boat for a while now and well not gonna buy the first sheet till I understand everything.

My question is this I have heard from a couple of people that if you are building a boat and you have a very long gradual rake from the bow to say mid way of a boat that this would make a boat faster is this true??? and that a fast turn down rake which would have the bow look of a barge would be slower boat correct?

Next question here say I am building a 15 ft long boat 44 inch wide bottom and say this a a flat bottom jon boat.

Let say I am going to do a slow gradual rake from the bow and have this rake stop say 4 foot from the stern of the boat and the bottom is flat and straight to the stern. I was told if I gradually raked it to either 4 foot from the stern or even 2 foot from the stern that this would be a fast boat but you wouldn't have much control is this true as well?????

How far could I make the rake from the bow to stern and yet have a ton of speed and a little control that is if this is all true to what i have been told by others or is this question more for an engineer or simply trial and error pretty much?


Again say a 15x44 flat bottom boat how much should the sides be angled out?? or does this all go by how narrow of a boat you're building?? WHats a good rule of thumb?

Just a few questions I have about building a boat I'm unsure about and I can't seem to find any info online about although am reading along the book by Stephen Pollard boat building with aluminum and haven't seen this yet in the book.

Hopefully someone can help answer my questions and understand where i'm coming from.

Thanks
Chris

 

Ok, you want to build a 15' x 3.75' scow hull with some flare.

Where do you want to operate? How fast do you want to go? How much do you want to carry (people, gear, and fuel)?

Scow hulls are very sensitive to these questions. Some of the things you listed above will work in some conditions at some speeds, but not all. Designing a good boat is making sure that the selected requirements work together...not just picking off a menu of different choices.

 

What do you call rake ?? are you refering to the vee of the hull or what !! the only rake i know in a boat is the rake angle of the transom to hang a outboard onto !!!

 

I'm not sure some if you will answer my questions since some may think this maybe to dangerous and it can be without the right safety gear but ok I'll tell ya what I'm doing. I've got a 75 evinrude short shaft motor i'm building this winter which once hopped up should be pushing close to 120 hp. I plan to drag race it.

This boat doesn't need to have a seat other then maybe a little bucket seat for me in the back, 6 gallons of fuel and the boat will be run in a calm river.

Maybe it is not called RAKE. I'm talking about the curvature of the bow to the bottom of the boat.

I'm not sure of what a scull boat is I'll have to look that one up. I'm debating still whether to build a totally flat bottom boat or a semi V boat with a pad or some call it a DELTA PAD. I'm just trying to understand if a gradual curve from the bow to mid ways or even further back to the stern will be a faster boat. I wish I had a clue how to operate program but can't get them to work for me.

Looked up what a scow hull is and it is nothing what I'm talking about. This is what I'm talking about http://www.alweld.com/custom_boats_flat_bottom.html
but changing up the rake or curvature of the bow.

For speed I want to go as fast as possible. I have a feeling I maybe just building it with my gut instinct and just have to do trial and error is what I'm feeling to be honest here because the last few times i have come on this forum it seems like i have not got the answers I want or maybe people didn't want to give advice for the fear i may kill myself I don't know.

 

totally insano !!!

WOW 120 hp on a flat bottom boat with a turned up front !!ARE YOU married and have a family ?? is so make sure you have a well paid up to date policy for the wife and kids .
If you not married make out a will !!

At the speeds you would be looking at with even a 75 hp it would fly and go straight up and flip over backwards for sure !!! totally insane like as in crazy !!
Have a look at Yucon river race sight thats more to what you should be doing !! they have it sussed and have lots a fun and a good time . some crazy people in crazy boats .

 

I've seen that but those boats are way to long. I know of a guy right now who has the same motor i got but with nitrous is pushing around 150 hp on 10 foot boat this thing is truly insane. I don't feel what I'm doing is that crazy. I mean you gotta be some what sane to even do it crazy will for sure get you killed.
If i build a boat and it doesn't work out I'll scrap it and build another.

I'm got a 50 Tohatsu on my current 15 foot but believe it or not my 75 hp weighs less then my 50 and produces more horsepower in stock form.

So can anyone answer my questions of the gradual curvature of the bow and how far back to stern could i go safely for control??

 

Chris,
The problem in answering your question is not defining the answer, but the question. What people are attempting to find out is what you really want to do and how much you know about boats so you can understand the answer(s). I think you are talking about rake of the bottom from the bow aft. In that case, this, as a design elment, has nothing, nada, zip, to do with speed. If carried to extreme, as you appear to ask, other things may make the boat either slow or dangerous though.

First thing to do is get a book or two so you can begin to appreciate what the different design elements are and how they affect the performance, both singly and in combination. Lots of designers make their living after years of study and work learning to juggle these elements to satisfy the goals set for the boat. Its not easy to reach that level of competence but it is not nearly so hard to learn enough to evaluate good design from bad. Even that comes with work though, so you need to be looking at some study.

On the other hand, there are many plans available for a pittance that will not only teach you much but guarantee a suitable boat. That is the best first step for anyone. A scow or jon boat is about as simple as there is so just looking at some examples will tell you what works and what does not.

 

Chris,

Forgot to recommend a book. One of the best to introduce a beginner to boats is Dave Gerr's "Nature of Boats" available inexpensively from Amazon or ABE Books. Lots of others to follow that with but this may be the best for you.

 

i have a small 14 foot fishing boat with a 115 vee 4 yamaha . it drives like a jet ski !!!

 

Chris, what you are talking about is called a hydosled. Developed for speed/racing prior to WWI, their speed greatly increased after the Great War due to advances in lightweight engines and the widespread use of stepped bottoms. Because of thier poor handling and habit of becoming airborne and flipping (as tunnels pointed out) they were abandoned for more modern 3-point hydoplanes. FWIW, I went to several drag boat sites and it looks like nobody is still running 'sleds.

One of the points about a 'sled is the need for bow-down moment, either by placing the engine and crew forward of the center of pressure or trimming the outboard heavily bow down. You will need some skeg strakes aft to keep it going straight and never turn at speed.

 

Chris, go to some of the racing forums and see what they are doing. ask your ?'s there and see what they have to say. not saying folks here do not know what is going on, they do, but ask the guys who race all the time who know what will happen if you understand what I mean.

Outlaw

 

Thanks Guys I will place an order for that book. I want to learn.

Outlaw45, I am here asking questions because one of the racing forum I go to that does a lot of small boat racing they either don't know or don't want to give up there hard earned secrets that have taken them years to learn which I can understand in a way but at the same time dam frustrating for me who is trying to learn to one day build a boat.

My current 15x52 alweld V hull boat I bought that I have put a 50 tohatsu outboard has taught me a lot. I've been playing with a jackplate the last couple of weeks and am hoping with setup and the correct prop i can go well over 40 mph. I will probably put this 75 on it and try it out once it's built but this 15 foot boat i have is more my fishing boat not my racing tear up destroy boat.

I have tried looking up the correct term of what I'm talking about but can't seem to find it and yall are right the rake is at the transom so I will stop saying that. I'll go do more digging and see if I can find the technical term and then come back. What I'm wanting to do I don't think is that hard it's just learning the technical terms so everyone can help me.

 

I believe the term you are trying to describe is rocker.
You are asking how the rocker of the flat bottom should be shaped for speed.

 

No I don't want any rockers or hooks on the bottom.

This is like what I want to try and build http://www.youtube.com/watch?v=0JGyku_oYiY

The owner of this boat won't give me much detail about the boat because his friend built it and is now dead but didn't die racing boats.
This boat is very pointy and has a very gradual curve from the bow to the bottom this is what I'm talking about.

 

Kengrome is his name... post number #6 on this thread he shows a drawing well three actually and the third drawing on the far right he says this is the the way the bow has a more gradual curve for more speed. I just wanted to know can I may it even more pointier for even more speed and at the same time should lighten the boat up more to?
http://www.boatdesign.net/forums/bo...0-bottom-flat-bottom-aluminum-boat-23639.html