Twin F mono

[tnrcboatracer]

I'm thinking about building a twin F mono. I was smitten by Ernie Lefluer's twin mono several years ago, and now I have a couple of MAC 84's that just need a home. I was wondering if it is better for a mono to counter-rotate the props to counter the prop torque? Anyone out there have experience with twin monos? Ernie, Steve how about some tips?

 

[Don Ferrette]

I'm thinking about building a twin F mono. I was smitten by Ernie Lefluer's twin mono several years ago, and now I have a couple of MAC 84's that just need a home. I was wondering if it is better for a mono to counter-rotate the props to counter the prop torque? Anyone out there have experience with twin monos? Ernie, Steve how about some tips?

Counter rotation on a twin mono is not the way to go, ask John Finch about that one. Had to edit this as I misunderstood John the last time we talked about counter rotation.

 

[Will Gallagher]

Jon,

I think a better idea for that pair of MAC 84”s would be to let me provide a loving home for them….

Will

 

[Don Ferrette]

Jon,I think a better idea for that pair of MAC 84”s would be to let me provide a loving home for them….

Will

The line forms behind me b*tch! :lol: :lol: :lol: :lol: :lol:

 

[1ernie lafleur]

I'm thinking about building a twin F mono. I was smitten by Ernie Lefluer's twin mono several years ago, and now I have a couple of MAC 84's that just need a home. I was wondering if it is better for a mono to counter-rotate the props to counter the prop torque? Anyone out there have experience with twin monos? Ernie, Steve how about some tips?

Jon Most of my success was done with both props turning the same way . This caused the boat to run on its right side which was sort of like running a flat bottom boat . "Take note to how Jerry Crowther runs down the straight" This leaning over to the right side also helped carve very quick corners .

When counter rotating was tryed , the lap times was never as quick . The boat seamed to handle better in race water cause it was riding on the "V" of the hull . With this more upright attitude corner speed was not as good. ERINE

 

[tnrcboatracer]

Thanks for the feedback Ernie. Counter rotating is complicated by the need for a rreverse rotation drum; does CMDI even make one? I'll call Andy on Monday.

Since I will be building the hull from scratch, the design is pretty open. I am thinking about a standard low profile 24* vee with strakes like a SD 3. I had planned on a shallow vee ride pad on the rear half of the keel. The ride pad would be a 10* vee angle ~1.5" wide with a strake depth of 1/4" where it meets the 24* bottom. The ride pad would be similar to that on a high performance bass boat.

I will make the props ~70mm apart to give 5mm gap between a couple of 65mm props. The shafts will exit the transom even with the hull bottom. The props will be within 3" of the transom. What about rudder placement; on center or off to the right? If I move it to the right, it will have to be 3" off center unless I put it up close to the transom (in front of the props.

Any thoughts on the hull bottom, prop layout, and rudder placement?

 

[John Finch]

I ran counter rotation a lot in the 1980s with several boats. Regular rotation works best like Erni explained. The no torgue idea doesn't work well when the boat rides loose because there is no torque to hold the boat steady. The boat tends to warble and hunt like resting a deep vee on a table. It falls one way or the other really easy. Since there is no torque to hold the boat on it's right side in a corner, the boat can go over on the high side too. While I found ways to compensate for the NO Torque problems, It's not worth the trouble.

 

[John Finch]

Thanks for the feedback Ernie. Counter rotating is complicated by the need for a rreverse rotation drum; does CMDI even make one? I'll call Andy on Monday.
Since I will be building the hull from scratch, the design is pretty open. I am thinking about a standard low profile 24* vee with strakes like a SD 3. I had planned on a shallow vee ride pad on the rear half of the keel. The ride pad would be a 10* vee angle ~1.5" wide with a strake depth of 1/4" where it meets the 24* bottom. The ride pad would be similar to that on a high performance bass boat.

I will make the props ~70mm apart to give 5mm gap between a couple of 65mm props. The shafts will exit the transom even with the hull bottom. The props will be within 3" of the transom. What about rudder placement; on center or off to the right? If I move it to the right, it will have to be 3" off center unless I put it up close to the transom (in front of the props.

Any thoughts on the hull bottom, prop layout, and rudder placement?

 

[tnrcboatracer]

I ran counter rotation a lot in the 1980s with several boats. Regular rotation works best like Erni explained. The no torgue idea doesn't work well when the boat rides loose because there is no torque to hold the boat steady. The boat tends to warble and hunt like resting a deep vee on a table. It falls one way or the other really easy. Since there is no torque to hold the boat on it's right side in a corner, the boat can go over on the high side too. While I found ways to compensate for the NO Torque problems, It's not worth the trouble.

Thanks for the reply, John. I'll use standard rotation. Do you have any thoughts regarding my hull design, drive line, or rudder placement?

 

[John Finch]

Rudder on the right was always non linear for turning. One rudder in the center worked well if it was at least 6 inches behind the props, which looks a little funny but was more consistant in the corners. Twin rudders just to the outside of the props worked best. Position them outside the prop rotation and just behind the props if you go with that setup. As for prop depth. You are right on. Even though you may think the left prop will starve for water when the boat banks to the right, it won't, because the water coming off the keel will fill the prop with water.

 

[John Finch]

I had written a whole lot but FLOOD CONTROL didn't let me get the messages thru. Thats why my post back a few didn't say anything. I guess the web is having a problem right now. I don't know much about these sites.

Ernie can probably tell you about what hardware setups work for him. His stuff is always right on. We tried the rudder in front of the props one time on a twin belonging to Steve Speas. That was his first and last twin. It didn't hardly turn at all. Seems like you need the leverage of having the rudder far behind the boat or two rudders to get linear turning every time at every speed. I like the 10 degree pad and 24 degree vee. I did however find a 24 to 26 degree vees to cause my boats to hunt at slow speeds. The 26 degree boat was really bad. The 21 degree vee was always the best. Maybe the 10 degree pad will eliminate that problem as my boats didn't have pads. I have build a 10 degree pad on my 20 straightaway boat but have yet to get the boat wet. Lets keep our fingers crossed on that one.

 

[tnrcboatracer]

10 dergree pad, huh......great minds think alike

I have also lofted a 22 degree vee design. maybe this would be a better compromise. BTW, teh hull will be 45~48" long with 12~13" beam.

I was having a 'net problem, too. I lost 2 replys to never land.

 

[bzubee]

Jon how about a twin cat? It would qualify as a twin for US-1 then?

 

[John Finch]

I ran the twin cats for a while and they were fun, but they will never get the job done against a rigger. I had a twin canard I designed about 20 years ago too. The problem with both is they run at a positive angle of attack. The riggers run flat or negative, which works a lot better at high speed.

 

[Don Ferrette]

I ran the twin cats for a while and they were fun, but they will never get the job done against a rigger. I had a twin canard I designed about 20 years ago too. The problem with both is they run at a positive angle of attack. The riggers run flat or negative, which works a lot better at high speed.

Ditto to that. I built two different twin cats and they were fun but like John said, no match for the riggers.

 

[tnrcboatracer]

Thanks for the input Bill, but I'll stay with a twin mono. It will compete in F mono. I'm going to start with a hull I lofted about 10 years ago while I was in Japan. It is closer to a Microburst than a Seaducer. At that time, I ran the strakes al the way to the transom. I see that most all of the fast hulls stop the strakes at the 1/3 point from the rear. I assume this is to anchor the transom in the corners. The strakes up front are to keep the bow from hooking, correct? I'll pull the first mold from the plug as it is, then I'll play with the strakes on the hull after I see what I have.

 

[bzubee]

Check the rules on the strakes some guys were talking up at the Nats how if strakes were ended at the transom they could be extra lifting surfaces. John Finch is our Mono technical person so check with him first.

Thanks for the input Bill, but I'll stay with a twin mono. It will compete in F mono. I'm going to start with a hull I lofted about 10 years ago while I was in Japan. It is closer to a Microburst than a Seaducer. At that time, I ran the strakes al the way to the transom. I see that most all of the fast hulls stop the strakes at the 1/3 point from the rear. I assume this is to anchor the transom in the corners. The strakes up front are to keep the bow from hooking, correct? I'll pull the first mold from the plug as it is, then I'll play with the strakes on the hull after I see what I have.

 

[tnrcboatracer]

I rechecked the rule book, and strakes going to the transom are OK. If the strake ends before the transom, it must be faired in. A square cut strake that ends on the bottom plane of the Vee is considered a lifting surface, and therefore illegal. I just noticed in the current wording that a ventilated hull is legal, as long as the steps are at less than 15* angle to the keel. I may have to try that on the ride pad or sides.

Jon, have you tried any 15* steps on your monos?

 

[John Finch]

See the monos are dead post. Steps are NOT legal in any way shape or form in IMPBA mono class. They are legal in offshore..