Liveaboard and old power boat

[sveinutne]

I am looking at several used boats in the 80’ foot size at reduced price. I am planning to use it as liveaboard and only move very slowly around, maybe at only 5 knots to save fuel. One boat got 2 x 1500 hp and use 600 liters per hours at cruse speed of 21 knots. Maybe that is the reason it is priced so low. Even at idle at 5 knots these engines might use a lot of fuel. I am thinking about taking one or both of the old engines out and replace them with some new small Yanmar at 100 hp. This might give me better fuel economy and a lot of space in the engine room that can be converted into something else.
It will give me a lot of boat for the money, and if I only visit marinas for fuel and water, the cost of keeping the boat could be very low. I wonder if I am forgetting something here?

[The Garbone]

Keeping an very good eye on the weather and that is a lot of bottom paint, ground tackle and 2 windlass.

[meme]

I will be very interested to hear what people in the know have to say about this. Would 200hp even move a boat that size without putting
too much stress on the engines?
I will be listening........

Originally Posted by sveinutne

I am looking at several used boats in the 80’ foot size at reduced price. I am planning to use it as liveaboard and only move very slowly around, maybe at only 5 knots to save fuel. One boat got 2 x 1500 hp and use 600 liters per hours at cruse speed of 21 knots. Maybe that is the reason it is priced so low. Even at idle at 5 knots these engines might use a lot of fuel. I am thinking about taking one or both of the old engines out and replace them with some new small Yanmar at 100 hp. This might give me better fuel economy and a lot of space in the engine room that can be converted into something else.
It will give me a lot of boat for the money, and if I only visit marinas for fuel and water, the cost of keeping the boat could be very low. I wonder if I am forgetting something here?

[Fiveslide]

I think replacing 3000 hp with 200 is a seriously flawed idea.

Differential power. You won't have any. When you engage a pair of 1500 hp engines turning massive props, stuff happens. Boat moves, generally where you want it to move. It spins and you dock your boat and you look like a pro.

When you engage a pair of 100 hp yanmars in an 80' boat turning tiny props. I don't think stuff will happen. I think the current and wind will have their way with you. And that's just at the dock. Who knows how it will perform in open water.

[sveinutne]

In 1927 my grandfather bought a 150 foot boat in Norway and put in a 50 hp diesel engine and sailed it to Singapore. It made 4 knots before too much started to grow on the hull. He had some problems before Gibraltar. Some head wind gave him negative speed, but except for that it went OK, so I think 200 hp will make it move, but the acceleration will be low.

[rw58ph]

Most major changes to an older boat is not worth tbe time and expense like changing engines. The potential fuel savings will not be near cost. The reason for the large hp is so the boat can go faster than hull speed about 9 to 10 knots. Besides fuel is a small % of the total cost of owning a boat.

Just run the boat at hull speed about and every couple of hours run at higher speed to get the engines up to operating temp. recommend operating temp is key impotence.

Also check with Marinas as to slips available and yard if they can handle

[rw58ph]

The Eagle is 58ft and powered by a single 165hp turning a 38" prop at 500 rpm. So two 200 would probably work. However it would be at hull speed. 9 total 10 knots.

There are two ways to power a boat large slow turning props or smaller fast turning props and. Most long range fuel efficient, have small hp engine turning large slow turning prop.

I personal would not by a boat over 60ft and under 50 tons.

[nimblemotors]

The problem you have with very large boats is they are VERY HEAVY and once they are in motion can cause massive damage when they crash into something. With a rubber-band powered motor, you can't stop them from crashing into and destroying everything in their path. You would want a tugboat to move it anywhere.

Cement boat slowly crashes into a marina destroys several boats - YouTube

[ranger58sb]

Originally Posted by sveinutne

I am looking at several used boats in the 80’ foot size at reduced price. I am planning to use it as liveaboard and only move very slowly around, maybe at only 5 knots to save fuel. One boat got 2 x 1500 hp and use 600 liters per hours at cruse speed of 21 knots. Maybe that is the reason it is priced so low. Even at idle at 5 knots these engines might use a lot of fuel. I am thinking about taking one or both of the old engines out and replace them with some new small Yanmar at 100 hp. This might give me better fuel economy and a lot of space in the engine room that can be converted into something else.
It will give me a lot of boat for the money, and if I only visit marinas for fuel and water, the cost of keeping the boat could be very low. I wonder if I am forgetting something here?

Find the fuel consumptions curves on those engines (as from the manufacturers) and then look at their prediction for 200 RPMs above idle speed.

See if you can find speed curves for that particular boat at specific RPMs levels; especially useful if you can find engine RPMs at theoretical displacement hull speed.

Coinsider a plan to run the boat at somewhere between 200 RPMs over idle up to whatever RPMs it takes to reach theoretical displacement hull speed.

(Generally, as long as you always run the engines at their correct operating temperatures... and occasionally run at higher RPMs, e.g., 80-85% load, especially if the engines are turbocharged... they should operate fine at those lower speeds.)

Compare potential fuel expenditures over time under that plan with the cost of removing the existing engines and gears, replacing with smaller engines and gears -- and shafts and props... etc.

All of the safety issues folks have cited are valid; when wind and current start moving a big boat around contrary to your direction, it often takes horsepower to overcome nature.

-Chris

[The Garbone]

Originally Posted by nimblemotors

The problem you have with very large boats is they are VERY HEAVY and once they are in motion can cause massive damage when they crash into something. With a rubber-band powered motor, you can't stop them from crashing into and destroying everything in their path. You would want a tugboat to move it anywhere.

Hey, It is not the skippers fault they build a marina in his turning basin..

[Tingum]

Bad idea. You would most likely break the small engines transmission when you put it in gear, it is not just the weight of the prop but the water resistance of the blades. If you did manage to get it going you could never stop it.

[sveinutne]

Nice video. I got the point. The engines are old, and I expect it might need some expensive overhaul, but if the engines can run efficient at low rpm, it will be good just to keep it. The only losses will the space I could get. Also 2 x200 hp might be better for safety.

[Pete7]

Originally Posted by sveinutne

[FONT=Calibri][SIZE=3] One boat got 2 x 1500 hp and use 600 liters per hours at cruse speed of 21 knots. Maybe that is the reason it is priced so low.

This sounds like a fully planning hull shape and as such will be rubbish trying to cruise at 6 knots. Think about small rudders designed to work at high speed, but will now be working at much slower speeds. A deep V or warped V hull design stuck at displacement speeds, not good when the weather turns.

Given your location and the need for large and cheap, I would look for a decomissioned fishing trawler, either converted or convert yourself.



MACDUFF - FAFB

Pete