out board size for cats

[Talbot]

Originally Posted by sv_makai

2 beautiful 27hp diesel yanmar ourboards in a boat that was designed for this setup. He to complained that under moderate seas and up the props woudl go air born and then plunge back in the water. In St martin last year we had to move the boats because of weather and the swells caused then problems and concerns as they couldn't motor off anchor and what tuned in a lee shore.

Very surprised to hear this. Yanmar make an ultra long leg for this engine , and on my catalac, the yanmar outboard skeg is the deepest part of the boat. The addition of planning wings also makes a big difference in bad weather.

Since I fitted this engine, I have not had any difficulty with cavitation, and I have been out in some bad weather. There are really only two problems with it, primarily the lack of electrical power (10 amps only) and also, the power curve is nearer to a car, then a marine engine,

[northerncat]

all of the easy cats(one of which i am building) are powered by twin yamahas and i have never heard of them having cavitation problems, therefore i am not to worried about this
sean

[northerncat]

seeing as the 9.9s are a high thrust low speed prop has anyone thought of putting a nozzle around the propellor to capture lost thrust? if you have ever maintained a jetski you know how important it is to not lose thrust around the prop tips

http://www.olds.com.au/marine/nozzles/nozzles.html

sean

[cat man do]

Sean, did exactly that on an F31 I was involved with building.

For the life of me I can't remember the brand, but it was off the shelf not custom , and alloy , specifically for the 9-9 and signal orange, same as the cat orange.

It did seem to make a big difference, but I'm sure it cost over a grand.

Hope this helps

Dave

[blkrk]

Hi there
E-tec has a model developed for the seal's and the likes in the early ninety's. It has a closed nozzle and suppossely has a higher thrust.
Mike

[Tnflakbait]

It really depends on the weight of your catamaran. I would go with the smaller twin outboards if the boat is 10,000 pounds or lighter. Beware of extra weight. I have a single tohatsu 30 on my 33' cat. I can get up to 11 knts full bore. Twins outboards is great for the manuverability and for the extra thrust of two props. It is also inherantly redundant. Cavitation is a problem on many cats because they ride over waves. If the props are suffeciently deep in the water it should pose no [problem.

[northerncat]

the two outboards are within a kilo of each other with i think the honda being the lighter so weight woudlnt be an issue, if all things were equal i would go the hondas but the yamahas have that very large gear ratio and i just wonder whether in the end this puts the ball in the yamaha court which is why i put the question on the forum
sean

[44'cruisingcat]

Northerncat, I did a little more investigation and the story I had heard that Honda's were being manufactured in Thailand was incorrect. In fact it was a mate of a mate who just happens to work at a dealer for a different brand of outboard who was the source of it. I am waiting for info about the "powerthrust" option on the BF20 Honda, and once again I think they are going to be my choice. The advantages of the Honda are :

20hp vs 9.9
703mm transom height vs 635mm - the prop is deeper in the water
power tilt vs manual with dodgy reverse lock down system

The Yamaha 9.9 does have a lower gear ratio and bigger diameter prop in it's favour, but 9.9 hp wouldn't be enough for me, and the 25HT's weigh in at 90kg EACH.......

[cat man do]

But will they stop you in reverse?

[northerncat]

one would think that with double the available horsepower you do with half the available gear ratio as you should be swinging a bigger prop, i hope that 44 is putting his boat in before mine as he could then give me some more feedback
sean

[44'cruisingcat]

Originally Posted by cat man do

But will they stop you in reverse?

As I said, Honda do have a High thrust, low pitch prop option, which is claimed to work well in reverse, with little or no cup to the blades. Honda also redirects the exhaust away from the hub in reverse. I have read of people with Honda 20's on cats and they all seem happy with them, but I haven't personally spoken to one yet. There's a local seawind 1000 with them, I am going to try to have a chat with the owner.

[44'cruisingcat]

There's an article in Multihull World #77 - a review of a Hughes EV14 which is powered by Honda BF20's. The boat is a 14 metre performance cruiser:

LWL: 13.5m
Disp light: 6200kg
heavy:7800kg
Cruise 1 engine: 7.5kt
2 engines: 9.5kt

They also say "the Honda's low down torque made for excellent down speed maneouvering under power."

[northerncat]

we'll have to have a discussion about purchassing motors sometime next year i think
sean

[northerncat]

would you touch these with or without a bragepole, check these out, theyve copied a yamaha 9.9 high thrust right down to having the parts interchangeable,
http://www.sailoutboards.com.au/ price in aussie at 2795
sean

[cat man do]

Originally Posted by northerncat

would you touch these with or without a bragepole, check these out, theyve copied a yamaha 9.9 high thrust right down to having the parts interchangeable,
http://www.sailoutboards.com.au/ price in aussie at 2795
sean

You've obviously found out some info Sean, how do they compare $$$wise to a Yamie/Honda, and are they a Yum Cha Knockoff or are they rebadged ??

Dave