Choosing Correct Outboard - Need Technical Help

I fitted two 25Hp to a 54 foot cat once. Yes totaly underpowered but I was'nt asked, just fit them.

He wanted a raising lowering job at the cockpit area. I built these two frames that held an ouboard and they slid up and down raising from water line to "almost: clear.

It was 2x50 mm 4mm wall pipes approx 1 meter in length held parallel by brackets above and below, the "transom" slide up and down.

Some kind of screw arrangement was going to be made but the owner decided to just winch them up and lower them down with his main sheet winch which was just above the devise.

In rough water the depth was insufficient and cavitation was a big problem. The engines were moved to pods on the stern --"I didnt do this" this of course made it worse and the engines were swamped. This poor boat of massive size with 14mm rigging never had a pair of decent engines in it.

It was sold and had fitted Vetus electric engines below with tiny 3/4 shaft. This system was supposed to charge the Batts when sailing by the props turning. He could not understand why folding propellers did'nt work!!! , Again a total disaster.

He set of to the Philippines and returned 3 days later complaining of under power and incapable of keeping them running. The boat was sold again.

She now sits in the marina as a floating condominium.

Outboards on cats is a bad idea. A couple of little Yanmars with shafts will increase the value of the boat more than the cost of the engines.

 

If you really wish to cut electric power consumption , a Propane reefer is a great (and EZ to be safe on a cat) choice.

"Also, wind is a waste of time because the wind gens don't put out enough amps on a continuous basis. They are terrible if you are anchored somewhere for a while. A good anchorage is, by definition, lacking wind."


Many folks never think that far , and few care about the 24/7 racket the blades produce for the rest of the anchorage!

The difference between 20hp and 25hp from the same brand will be hard to realize , but there is usually a big price difference.

Save !

FF

 

Thanks, FF.

I am a big proponent of propane refrigerators and have been living off a nice Norcold 3 way refrigerator and freezer since moving off my last catamaran. It's a fantastic refrigerator and it keeps ice cream nice and frozen. Food lasts way longer and it just plain works better than most marine systems. Opening the front is a bonus too.

But... in the real world living at sea, there aren't any propane fill ups at the dock next to the diesel and gasoline pumps. If there were, this is the route I was going to go.

Since you can't fill up propane without renting a car, you're pretty screwed each week when your 5 gallon propane tank runs out. Solar refrigerators and freezers (well, electric, powered by a big solar array) are the way to go on sailing boats. They work about as well as a home refrigerator on land in that you don't even have to do anything except enjoy cold and fresh foods.

I think I'll crack open a new thread about mounting the outboard now that we have them selected. Thanks for that input on the "rule of thumb" - it seems to agree well with other input.

 

you're pretty screwed each week when your 5 gallon propane tank runs out

Time for a better propane fridge , or a good tune up on your existing unit.

Our large Dometic 1960's setup with fridge and freezer above runs 20-25 days on a single bottle in summer heat..

The new units are better and will go 30 days , even with a propane range in the circuit.

4 tanks , 4 months , not a big deal.

ALL box fridges will operate better with 2 inches of foam glued on the sides and front door.

The "best" in good sized units are the Servelle , made for Amish folks with houses (so the factory insulation is thick ) not for RV's where interior volume is more important than outside dimensions.

FF

 

I might be off on my recollection of consumption, but I've been plugged in and working on the boat for quite a while.

Maybe it was 3 weeks.

It was weekly for my propane heater.

Anyway, you never have to haul propane and rent cars with solar. It just always works. Much less hassle.

My refrigerator is a brand new Norcold n641. It runs just fine.

Here is a link to some consumption figures. The new Servel (which is made by Dometic) uses 1.1 lbs of propane every day. So, 3 weeks for 5 gallons, same as mine.

http://www.gas-refrigerators.com/servel.html

 

"with solar. It just always works. Much less hassle."


Yes BUT , the electric power consumption of an absorbtion fridge is HUGE!

In an RV it only is used with the engine ON , so (20-25A, 12V) no cares. Or in a campsite where 120V is provided , so again no cares.

In electric it will use the same Power as when on propane , but each gallon of propane has about 90,000btu.

Frightening to do the math! And think you will need that much electric!

FF

 

Not sure what you are talking about.
Nobody uses gas adsorbtion refrigerator in dc mode on a sailing vessel.

 

"Solar refrigerators and freezers (well, electric, powered by a big solar array) are the way to go on sailing boats. They work about as well as a home refrigerator on land in that you don't even have to do anything except enjoy cold and fresh foods."

From this statement I assumed you would be attempting solar power for an absorbtion fridge. My error.

If you want to count on the fridge , look up the
www.rvstuffusa.com/rvrefrigeratortesterbydinosaurelectronics.html
circuit boards as a replacement.

The Servelle has NO circuit boards ,as well as great insulation, which is why I always suggest them instead of RV units.

 

Whoops! I suppose we were talking about two different things. The confusion is that I currently have a Norcold on my RV I live in while building the boat.

I would not have and adsorbtion fridge running on the boat in DC mode, as I know what you mean about consumption there.

Are they make the Servelles the same way they used to, or are they cheaping out now that they're Dometics?

 

"or are they cheaping out now that they're Dometics?"

I believe they have were sold , as a seperiate product for decades.

The advantage of the Servelle is the lack of an electronic control , that is unreliable.

THe control is RV gear that hopes to shut down the propane operation of the unit in a gas station for legal reasons.

Servelle is home gear , heavier insulation , and manual start .

On a boat the RV exhaust cap system is useful as these units are sensitive to having the exhaust requirements exactially filled.

 

Yeah, I know about the exhaust. My RV is custom made (by me). I had a previous RV I built a well. Both had the Norcolds and with both, I had to build a quite complicated baffle and venting system, as per the instructions.

What do you mean about the control shutting down the flame at gas stations? My Norcolds (neither of them) care what's going on with the RV. They just do their thing, cycling on and off when the temp in the box requires it.

 

the control shutting down the flame at gas stations?

On most the circuit board when the unit is running on 12V notices when the engine is shut down , by the voltage drop.

They then block the propane operation for 20 min , worried that you are in a gas station.

120V use in as in campsite is not blocked .

FF

 

And don't underestimate the propeller equation.
Take several with you until you find the right one.
Lister

 

Wow. I would have been quite upset if my refrigerator came with that "feature." The Norcold n641 does not work that way.

 

Do the outboard sales folks usually allow you to try props if you buy 3 outboards at a time?