Motor position on transom

[Ram4x4]

On a boat with an offset cockpit, should the motor be mounted in the middle of the boat width, or set to the middle of the cockpit?

[DiGia54D]

When I ran CMH with my Hemp boat the motor was centered with the middle of the boat, was NOT centered on the transom. But I guess it would depend on how much the cockpit if offset

[hoosier]

If you mount it in the middle of the cockpit , there won't be enough room to drive the boat .

[runabout333]

LOL... Then it becomes an inboard..

[T Chance]

When I finished my granddaughter's K-Pro B&H Kit, I asked Sam that very same question and his answer was: "Yes."

[Jack Stotts]

I'd start out centering it on the boat. Get a good speed reading but also evaluate the handling. Then try it centered on the cockpit. A good friend had his centered on the cockpit and found it difficult to control the boat. He then centered it on the boat and solved the handling issues and picked up 2 MPH. This may vary between different boats. Jack

[Ram4x4]

So basically, try it and see....okie dokie.

And for the comedians, I thought about what I said and figured someone would point that out :-)

[hoosier]

Sorry man couldnt help myself , you going to Alexandria this weekend ?

[Ram4x4]

No, unfortunately, I have a lot of work to do on the trailer I got when I bought the boat at grass lake. Needs tires, needs new decking, rails and clean up. then I get the envious task of fighting with PA DMV to try to get a plate for it (no title, no registration, etc since it came out of WI). PA is very anal about taking as much money as they can from you to register vehicles and trailers.

[runabout333]

Ram4x4......... You actually said it right in your first post.. The key element is "middle of the boat width."

[gabengail]

It is actually a personal choice. I have had both. on the one with offset cockpit (1 inch), I centered on Cockpit with no ill affects. One my current hydroplane with centered cockpit, I shade the engine to the left from a 1/4 to 1/2 inch. I have seen OSYs run with engine mounted to the very left side of the cockpit. You have to see what the boat and you like.

[Team B&H]

Of course the answer is YES as Tim Chance relates. Only you are able to answer that question to your own satisfaction so you have to make a couple trials- just as you should have to do with engine height and kick-in angle. There are too many variables to have a concrete answer. Or you may find it's a lot like gas/oil ratio, in that it doesn't make as much difference as one might imagine. It is pretty easy to move the motor around unless you have a thrust block mounted to the transom. And you may find out how it effects things, you might want to run it in different locations as influenced by the race course. Oops, that darned thrust block again! And you thought you asked a simple question and would get a simple answer?

[Ram4x4]

Well, short of an "It must be mounted dead center of the boat or it's dangerous" type answer (which is what I was primarily wondering), then I fully expect it to be like everything else in racing...it depends....

[pops67g]

I run my D centered on the cockpit. There is no problem with tracking on the straitaway and the turns are VERY good. Now turning right is a whole other thing, but then we don't do that do we?

[Graham]

Can someone explain what the purpose is for an offset transom?

[Ram4x4]

It's the entire cockpit offset to the left (and thus the transom as well), it gets your body weight moved over more to the left supposedly for better turns. Kinda like how sprint cars do the same. I'm sure we could have a prolonged discussion as to how effective it really is.

[johnsonm50]

How effective offsets are would probably have to do with the courses they run on as well as how offset they are, short courses or narrow turn course would seem to be where they would do well... if it makes a difference. A top driver would do well in either.

[Ram4x4]

Yeah, I think the only way to get any real world measurements would be to test an identical hull, one with offset and one without and see how the lap times compare. I don't know of any other way to measure effectiveness. Of course, there are other things racers do too that help, or at least it is perceived as helping.

I've been reading heavily about treatments and shape of the bottom one can do to help with boundary layer flow. The consensus is that sanding the bottom to slightly roughen it doesn't really help the water flow better, but it does help to break surface tension if the intent is to get that portion of the boat up out of the water easier, like we do when weight shifting back to get the front to fly. The problem is that the treatment has to be on the areas that will fly and that area changes with conditions and speed. So, does sanding the back area of our bottoms really help? Not according to those guys.

Bottom shape is most important they say and as flat as possible is the ticket. Some sort of step or steps would be more helpful to introduce air turbulence to break surface tension. The intent with a hydro is get it up out of the water, vs trying to make it slip through the water.

These guys also point out that layer separation along the sides causes more drag than the flow along the bottom. Having air traps that go all the way to the rear helps more with controlling the layer off flow than sanding does to make the boat "slicker". It also helps to keep air pressure up to lift the boat, also decreasing the drag effects.

So, does sanding the rear portion of the bottom help or not? I dunno, but it seems a lot of racers do it.

I think offset probably falls somewhere in this realm. Does 1 or 2 inches of offset really help?

I can say after driving three different hulls, all with centered cockpits and then driving my boat, the differences in feel were significant. On the first three boats, I found myself cranking the wheel at least a good half turn or better to get them to turn hard. My boat only needed about a quarter turn of the wheel and on my first race in it I went past the first pin and then zipped right inside the second pin lickety split. Was that due to the offset? Maybe, but I also had the motor centered on the transom, so it could have been the result of the motor being offset more than my weight, or a combo of both.

When I get my boat out on the water again, I'm definitely going to try centering the motor on the boat width and see how it feels.

[ZUL8TR]

Yeah, I think the only way to get any real world measurements would be to test an identical hull, one with offset and one without and see how the lap times compare. I don't know of any other way to measure effectiveness. Of course, there are other things racers do too that help, or at least it is perceived as helping.

I've been reading heavily about treatments and shape of the bottom one can do to help with boundary layer flow. The consensus is that sanding the bottom to slightly roughen it doesn't really help the water flow better, but it does help to break surface tension if the intent is to get that portion of the boat up out of the water easier, like we do when weight shifting back to get the front to fly. The problem is that the treatment has to be on the areas that will fly and that area changes with conditions and speed. So, does sanding the back area of our bottoms really help? Not according to those guys.

Bottom shape is most important they say and as flat as possible is the ticket. Some sort of step or steps would be more helpful to introduce air turbulence to break surface tension. The intent with a hydro is get it up out of the water, vs trying to make it slip through the water.

These guys also point out that layer separation along the sides causes more drag than the flow along the bottom. Having air traps that go all the way to the rear helps more with controlling the layer off flow than sanding does to make the boat "slicker". It also helps to keep air pressure up to lift the boat, also decreasing the drag effects.

So, does sanding the rear portion of the bottom help or not? I dunno, but it seems a lot of racers do it.

I think offset probably falls somewhere in this realm. Does 1 or 2 inches of offset really help?

I can say after driving three different hulls, all with centered cockpits and then driving my boat, the differences in feel were significant. On the first three boats, I found myself cranking the wheel at least a good half turn or better to get them to turn hard. My boat only needed about a quarter turn of the wheel and on my first race in it I went past the first pin and then zipped right inside the second pin lickety split. Was that due to the offset? Maybe, but I also had the motor centered on the transom, so it could have been the result of the motor being offset more than my weight, or a combo of both.

When I get my boat out on the water again, I'm definitely going to try centering the motor on the boat width and see how it feels.

Much research being is done to reduce air and water drag to reduce fuel costs, etc. The skin of fast moving sharks is not smooth but has dermal denticles for reduced drag and copied and known in the research as surface riblets tape developed by 3M for the America Cup Stars and Stripes:

https://www.nasa.gov/centers/langley...s/Riblets.html

Since you are interested in the drag reduction theories here is an interesting research paper you can browse (heavy in the math but there are pictures ;-) :

http://rsta.royalsocietypublishing.o.../4775.full.pdf

The riblets theory is similar in application to planning bottoms sanded in the fore aft direction. The grit size is a matter of choice. As with all things in nature testing is required.