Trueing up the bottom of a mono?

[Jarcaines]

Okay, so I am working on restoring my A Mono and I know what’s important on the riding surfaces of a hydro or a tunnel hull, but what is the priority on the bottom of a mono? Does the keel need to be a very sharp edge? Do the strakes need to be perfectly sharp and squared off at the end? Or is my main concern just that the bottom cuts off at a sharp 90* angle at the transom?

Sorry if this is a dumb question. You only learn from asking the right people.

 

[David Ashcroft]

Sharp strakes and transom edge is very important ,,

True the last 6-8" of the bottom hull .a flat hull is a fast hull.
After it is flat even ,compliment with a scratch of 300-400;grit to help loosen up the hull.

Basically take out hooks and concaves

 

[David Ashcroft]

You can for experiment purposes round the the strake edges for a more comfortable less aggressive bite on the turn..

 

[john v]

if it is a seaducer then its a different plan

 

[Jarcaines]

if it is a seaducer then its a different plan

It’s not a Seaducer, but how so John?

It’s a JD Mono, so maybe @Jerry Dunlap has some advice?

 

[john v]

It’s not a Seaducer, but how so John?

It’s a JD Mono, so maybe @Jerry Dunlap has some advice?

seaducers have a built in hook on the bottom, this is why ducers do not need trim tabs, well the smaller boats do not, i believe the big gas boats use tabs. if not a ducer then make sure the bottom is flat and sharpen the transom to the bottom as well as the strakes, scuff or break the shiny gelcoat on the running surface. tower hobbies sold a nice aluminum bar sander with self stick sandpaper that i like. this method works for me but you might get some other opinions

 

[Chris Wood]

my dad had a seaducer that dunked none stop. ran super flat and BAM.. we messed with props struts ect.. we finally put bondo on the bottom at the very tail end about 6" or so. and started to sand.. bit by bit.. must have used over a gallon in fuel till we got it JUST RIGHT. it was great then turned excellent, flat very nice running. But like i said we had to do some work.. Remember these are fiberglass and in molds.. if you don't take your time when you are laying things up it can change.. We must have gotten one that was off.. You don't want to remove all the reverse hook on the bottom but there is a balance to how much you can before you go to far.

If you have a seaducer just keep that in mind.

 

[ChrisHerzog]

my dad had a seaducer that dunked none stop. ran super flat and BAM.. we messed with props struts ect.. we finally put bondo on the bottom at the very tail end about 6" or so. and started to sand.. bit by bit.. must have used over a gallon in fuel till we got it JUST RIGHT. it was great then turned excellent, flat very nice running. But like i said we had to do some work.. Remember these are fiberglass and in molds.. if you don't take your time when you are laying things up it can change.. We must have gotten one that was off.. You don't want to remove all the reverse hook on the bottom but there is a balance to how much you can before you go to far.

If you have a seaducer just keep that in mind.

I may be wrong but the earlier Seaducers dunked because of the slope of the deck. I ran into the same problem with the Hurricane mono. With a peanut motor (a mod 23) they were fine but when the 260 came out and people started modding them the extra speed caused to much down force on the nose of the boat and if the prop came unhooked they would dunk.

When you sand on the bottom of a mono, a lot of guys make this same mistake. These guys will sand the hull from front to back and check the hull with a straight edge only from front to back. You need to be mindful and also check the hull from the keel to the chine. So after you check from front to back you have to check the bottom keel to chine as far as you can go forward until you get to the strakes. Then you should also check the bottom again in both directions on a 45 degree angle. That is the only way to truly get any hooks out. Unfortunately, because of the way some hulls are made, it sometimes can’t be done at all unless you remove the strakes completely. Then if you do that, you would have to make new strakes and put them on the boat after you have gotten it squared, a royal pain and a lot of work!!

 

[ChrisHerzog]

Pics are better then words.

 

[john v]

great pics chris, thanks

 

[ChrisHerzog]

great pics chris, thanks

Thanks. Vid would have maybe been better but I think guys can see what I was talking about.

I should also add that I move the straight edge all over the bottom of the boat at these angles to check as much of it as I can. The more you check the better the bottom will be as a whole.

 

[john v]

pictures are really worth a thousand words

 

[Jarcaines]

Thanks Chris, that’s very helpful.

 

[donaldhuff]

The only good way that I have found to get the bottom truly flat is to remove the strakes completely. That way I can use a long wide sanding block and bondo, and get the surfaces FLAT! Don't worry about replacing the strakes either, they serve no purpose on our models.

I have removed the strakes and flat chines on a few hulls, but a couple of them refused to turn left no matter what I did to the hardware. I added a flat chine about a 1/4" wide to the left side, and it turned like it is supposed to do. I have now put puddy in the strakes in my mold so that I don't have to sand them off anymore.

Do make all edges as sharp as possible on the transom and chines. The keel is not so specific, some like it sharp while other hulls will like it rounded. But either one will do better with the keel rounded on the front say 30% (the curving up part and blending into the flat part). This will allow the nose to slide a little in the turns. Credit for this mod goes to John Finch.

 

[Robert Krescanko]

And then you have a hull such as the Assault mono that has hooks built in for a reason.