What is the best Catamaran to cruise and retire on?

[Dymaxion]

Best answer I can give to the OP's question...

Someone else's!

PS: This answer also works for another common question, namely...

What is your favorite boat?

[sailorcherry]

Yep, I told him they were in the wells in the cockpit, perfect location and positioning. He is still learning cats, very monohull educated though.

Okay, how about the noise though between the H8 you had versus the Yamaha? I could see that swaying people.

That is hilarious, well not really, the illistration of the Somali pirates....for Yammies.

I have a Honda 9.9 HT, 2005 or 06. Long shaft. Bought it off a guy selling it to debt against his new Y9.9 HT, we got to compare them in person, not running both, man what a difference in prop.

Can someone help me understand, please, why higher thrust at lower rpms makes the Yamaha better over the Honda?

Btw, if you did put bigger motors on your 36 what could be your max speed? And where the hell were you in the 72 kts wind? A hurricane in the Carib?!

Originally Posted by schoonerdog

The 36 has OB in the engine wells inside the cockpits, so it's well forward, where it should be. I've owned Tohatsu, Nissan, Honda and Yamaha. They are all good, though I think that only Yamaha has an EFI on a manual start 25 HP engine, and they are lighter than the rest for a 25HP. It's quiet an engineering accomplishment. As to being under powered, the PDQ36 is 8000 lbs, with and 11 to 1 or so hull beam ratio for the hull itself, so they have very narrow hulls and go through the water very well. I've been in 72 knots of wind with the PDQ, head on, and while I wasn't making headway, I wasn't being pushed back either. With both of them going I could probably do around 8 knots, so I wouldn't call them underpowered. And you do want the low RPM high thrust model. Yamahas are everywhere once you leave the US. I couldn't find spark plugs for my Honda 8, but anything Yamaha was to be found in every small port. Just look at any video showing Somali pirates in a skiff being blown up and you'll see they are driving a Yamaha! But again, I think they are all good engines. The only bad engine I had was and Evinrude, their poor attempt at a 4 stroke in the 90s that made them go bankrupt. That was a truly horrible engine.

[liquidice]

Originally Posted by sailorcherry

..



Can someone help me understand, please, why higher thrust at lower rpms makes the Yamaha better over the Honda?

I think I know this one. So think about an outboard and what most people buy it to do: put a boat up on a plane.

Most outboards are designed to push something relatively light (compared to a sailboat with ballast) fast enough to get it planing and exceeding hull speed. Sailboats use outboards to get up to hull speed, no more. The high thrust motors can push a heavier boat more efficiently, but won’t have as high of a top speed if they were used on a planing boat.

Like having a bike that stayed in a low gear. Easy to get going, impossible to get going fast. Perfect for a displacement vessel like a sailboat, which can’t do a “hole shot” and get up on a plane anyways.

[44'cruisingcat]

Originally Posted by liquidice

I think I know this one. So think about an outboard and what most people buy it to do: put a boat up on a plane.

Most outboards are designed to push something relatively light (compared to a sailboat with ballast) fast enough to get it planing and exceeding hull speed. Sailboats use outboards to get up to hull speed, no more. The high thrust motors can push a heavier boat more efficiently, but won’t have as high of a top speed if they were used on a planing boat.

Like having a bike that stayed in a low gear. Easy to get going, impossible to get going fast. Perfect for a displacement vessel like a sailboat, which can’t do a “hole shot” and get up on a plane anyways.

Yes, but not the entire answer. If you put high thrust props on a Honda for instance, then it will be geared for slower than planing speed too.

The advantage the Yamaha high thrust motors have is that they use bigger gearboxes with deeper reduction gearboxes so they can spin bigger diameter props with a fair amount of pitch at lower revs.

This gives the props better "bite" and greater efficiency at low speeds.

[catsketcher]

Originally Posted by sailorcherry

Y

Can someone help me understand, please, why higher thrust at lower rpms makes the Yamaha better over the Honda?

I have had both the Yammie 25 and a Honda 25. The Honda was lovely and smooth 3 cylinder engine but had poorer reverse and less grunt. When we got the Yammie we couldn't get the anchor to set at first because giving it the same reverse revs as the Honda just pulled it out of the bottom.

There is some Physics in why the Yammie has better grip and performance.

- Prop area. The prop has to push a cylinder of water backwards to push itself (and the boat) forwards. The Honda had a 9 inch prop and the Yammie a 12. This gives the Honda 63 square inches of prop area and the Yammie 113 square inches. So the Yammie has almost twice the area to push on the water. This is best felt in gusty conditions. With the Honda our cat would slow appreciably. With the Yammie she powered through the gusts and would not just make a milkshake with the prop.

Also there is some other Physics here too. Newton's third law is how props work. The prop pushes backwards so the water pushes forwards. So why not have a half area prop and push the water twice as fast - it's the same right?

Well no- Although you will get the same force (as long as the prop grips well) it will cost you more in fuel to do so. The energy of moving objects is KE = 1/2mv^2. So to move the water twice as fast takes 4 times the energy from the motor. So on our slow boats we really want the slowest possible and largest props to be efficient. Small props work well on light tinnies that go fast but not on our large boats. So the Yammie with its reduction gears can save you fuel as well as aggro in reversing situations.

Probably one reason why diesels are more efficient than outboards is that some can swing a massive prop (there are other reasons as well) - up to 17 inches for a 40 footer. Compared to our Yammie's 113 square inches this gives the diesel exactly twice the area - 226. That means they can push the water at half the speed my Yammie for the same force which is 4 times more efficient. If only Yammie would bring out a monster prop version I would be very happy.


cheers

Phil

[liquidice]

These responses have real value to me. Thanks. I repair old outboards and this helps me understand the physics behind them better.

[Morph]

My boat has two honda 20s and they were amazing!!! Would totally go for them again for all the reasons stated above. I put the high thrust props on and fully loaded up I still got 9 knots out of here . Normally I'd cruise at around 6 knots and use a lot less fuel.

The idea of no anodes, no expensive folding props, not fuel bug, no drag all at 1/3 of the price.... and then changing them over when it's time is actually pretty easy

[Morph]

PS, I have never got my head around the high thrust props/gearbox of the Yamaha 9.9 vs the Honda 20s--however, I know the honda 20s did an amazing job on my boat.

[44'cruisingcat]

Well, put it this way. The high thrust 9.9 Yam will do a better job than a Honda 10. Maybe better than or similar to a 15.

But Yes, the Honda 20s with the 28 inch shaft and powerthrust props do work well.

[44'cruisingcat]

Originally Posted by catsketcher

I have had both the Yammie 25 and a Honda 25. The Honda was lovely and smooth 3 cylinder engine but had poorer reverse and less grunt. When we got the Yammie we couldn't get the anchor to set at first because giving it the same reverse revs as the Honda just pulled it out of the bottom.

There is some Physics in why the Yammie has better grip and performance.

- Prop area. The prop has to push a cylinder of water backwards to push itself (and the boat) forwards. The Honda had a 9 inch prop and the Yammie a 12. This gives the Honda 63 square inches of prop area and the Yammie 113 square inches. So the Yammie has almost twice the area to push on the water. This is best felt in gusty conditions. With the Honda our cat would slow appreciably. With the Yammie she powered through the gusts and would not just make a milkshake with the prop.

Also there is some other Physics here too. Newton's third law is how props work. The prop pushes backwards so the water pushes forwards. So why not have a half area prop and push the water twice as fast - it's the same right?

Well no- Although you will get the same force (as long as the prop grips well) it will cost you more in fuel to do so. The energy of moving objects is KE = 1/2mv^2. So to move the water twice as fast takes 4 times the energy from the motor. So on our slow boats we really want the slowest possible and largest props to be efficient. Small props work well on light tinnies that go fast but not on our large boats. So the Yammie with its reduction gears can save you fuel as well as aggro in reversing situations.

Probably one reason why diesels are more efficient than outboards is that some can swing a massive prop (there are other reasons as well) - up to 17 inches for a 40 footer. Compared to our Yammie's 113 square inches this gives the diesel exactly twice the area - 226. That means they can push the water at half the speed my Yammie for the same force which is 4 times more efficient. If only Yammie would bring out a monster prop version I would be very happy.


cheers

Phil

The problem with pushing the water at less speed is that there comes a point where it limits the speed of the boat. Ie if you push huge quantities at 4 knots, you might have plenty of thrust, but you can't go any faster than 4 knots. Only slower.

This is something some electric motor salesmen seem to overlook. They talk endlessly about static thrust. But you can achieve huge static thrust by having a very large, slow turning low pitch prop, yet it could be quite useless in terms of driving a boat forward at an acceptable speed.