# Transom and side angle?



## fishbum (Jan 6, 2013)

Have been looking at some stuff on boats for awhile.
What is the relationship of the side angle on a boat to size or type of motor 
On the boats I have had if you look at the rear the side angle is about 35-40 deg
Goes from 66" at the bottom to 90" at the top with 27" sides
If we look at say a river pro hi pro, there is not near as much angle?
I wonder what effect it has on speed, draft ect.
Is it just trying to keep the hull under a certain size?
I would think it helps with how shallow draft you have?
I guess I have too much time on my hands!


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## Darkside (Jan 7, 2013)

Fishbum- I understand the thought process. 

I had a friend with a small shop that did as much insurance repair work as they did new boats. They averaged only 12 new boats a year with 19 being the most in any one year. These were true custom crafts built from the ground up. Sheet aluminum formed with jigs and welds.

The owner let me play with creating boat chine jigs and even creating bow shapes for Modified V and Dory shaped bows on the 3 aluminum jet boats I purchased from him. I was able to assist and at times have complete access to the shop while he was away. As you can imagine, I made a good many mistakes and items that hung on the shops “wall of shame”. I also learned a tremendous amount along the way and about 4 ways NOT to shape a jet tunnel. 

Transom Flare and Transom Rake have two very different impacts on a boat. For outboard jet crafts, it is easy to get into trouble with too much or not enough rake (angle). Amazingly, even a modest difference a transom wedge can make is enough to create a few extra miles per hour or create significant cavitation. I will not give the angle we found best because this builder still has a boat business LOL, but you can be easily caught with not enough angle or too much. 

Transom Flair, meaning the amount of pitch angle the boat side comes out from the chine (bottom) does play a role. We discovered that no less than 6” or more than 9” from the bottom to the top of the transom where the side height was 22-24” worked best. Where you will notice the most on a river or lake is rolling into a still eddy from fast/hard current, or coming off a high wake chasing a boat running in the same direction, or coming diagonally across large wave swells. It is that uneasy feel as the craft slowly shifts from one side to the other. The more the transom flares, the more rock you will feel. Look at the shape of a steel barge sometime. Shops that have the ability to increase the flare moving closer to the bow (or inverse – high flare angle in the bow and low angles as it reaches the stern) is the way to go. 

Likewise, a hard chine is critical from at the very least the last half of the boat. I know people like to speak volumes of hard chine verse soft or rounded chine, but the chine can change to soft or rounded and still serve the craft well. I’ve never been a big fan or soft (round) chine crafts where the extend into the transom (back half of the craft). Ever try to cut canned peach halves with a spork? That is the best visual I can provided when trying to turn / maneuver a completely soft chine craft with jet power. Imagine hull performance similar to a snow ski with rounded verses sharp tuned edges. Few slalom races were ever won on dull or rounded edges! 

What is lost on most on people is the value of deadrise in a boats bottom. In simple jon style sleds, the max transom deadrise is 3-6 degrees and slowly degrades to near nothing in the bow entry. Shops with more sophisticated tooling can allow the dearise to maintain through the bow or in some cases increase as it enters the bow. These crafts usually take the performance cake regardless of prop or jet power. When it comes to draft, it is hard to argue against lower deadrise angles. Problem is that low deadrise bottoms do not handle speed or even the slightest chop well. There is a balance.

Bow Rocker, that dip or drop you notice in the bottom or the boat as the aluminum or fiberglass rejoins left tor right sides as the bow is formed is tricky. I don’t have enough experience there and am always concerned at how a craft will perform after rocks drifting or running in shallow river start to “season” a hull with a large rocker. By season, I mean DENT (laughing).


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## fishbum (Jan 8, 2013)

Darkside said:


> Fishbum- I understand the thought process.
> 
> I had a friend with a small shop that did as much insurance repair work as they did new boats. They averaged only 12 new boats a year with 19 being the most in any one year. These were true custom crafts built from the ground up. Sheet aluminum formed with jigs and welds.
> 
> ...


Chris, Thanks for the input. Im sure I know who you are talking about with the boats, I have been trying to get the hull I have now to run right can't get rid of the cavatation on take off, been playing with tunnel but found a rise in the cebnter of the hull about 12" in front of tunnel that looks like a rock dent but is not. think it was something to do with how the tunnel was cut in and finished that made the floor hump up. don't know yet if it is doing the deal with takeoff
but can't be good, the hull feels to me like it has a hook angle in the rear pushing the bow down. getting the hammer out now!


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## Kevin Turner (Jan 10, 2013)

fishbum said:


> I guess I have too much time on my hands!


 Then go fishing! LOL

Hull design cause and effect can be a bit tricky. Thoughts are swirling though my head, but my slow typing keeps me from responding...


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## fishbum (Jan 10, 2013)

Kevin Turner said:


> fishbum said:
> 
> 
> > I guess I have too much time on my hands!
> ...


You are right! more fishing less brain work. I guess your Hi Pro is is what made me ask the question about side angle.
yours doesn't have much. at least not like standard jon boat hulls. (mine)


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