Engines

by David Lincoln

Engines

Jolly Roger
Advanced Member
Jolly Roger
Advanced Member
Joined: March 11th, 2006, 3:16 pm

October 29th, 2007, 5:22 pm #1

Engines

There are basically 3 types of engine configuration to be found on the Evolution 26.


https://flic.kr/p/YpRSyT
Outboard Motor on Transom


This is perhaps the simplest configuration. It is particularly well suited to racing boats, as a small (say 5HP) engine can be used to get you out to the start line. This can then be raised up, leaving a very streamlined hull underneath. Some people remove the engine and put it inside the cabin with the anchor when racing to keep the weight off the ends of the boat (the keen ones!).

The advantages of this configuration are:

The propeller can be raised out of the water completely when racing to reduce drag.
Bottom of the boat is smooth.
Prop won't get damaged when drying out.
Can take the engine home in the winter for a service.

The disadvantages of this configuration are:

Propeller can come out of the water losing drive in a rough sea.
May come out of the water when motorsailing on port tack.
You can't use prop wash on the rudder to manoeuvre the boat in a tight berth (although you may be able to steer the engine)
Vulnerable to theft.
Not ideal for cruising as you will need at least an 8hp engine. Only really practical to go for a 2-stroke mounted on the transom as a 4-stroke 8hp will be too heavy.
Difficult to lift over the pushpit to store in the cabin.
Difficult to stop the boat in reverse.


https://flic.kr/p/YpRS5r
Outboard Motor in a Well


Many Evolutions including mine have a well on the centre line for the outboard.

The advantages are:

Weight is further forward than if the outboard is mounted on the transom. Can therefore fit a quieter and more fuel efficient 4-stroke (mine does better than 2 litres per hour at 5.5 kts)
You get the benefit of prop-wash on the rudder for tight manoeuvring
Outboard less prone to theft as it isn't as visible as an outboard on the transom.
Can be raised slightly to prevent prop touching ground when drying out (see centre picture above)
The well forms a big cockpit drain. Cockpit clears instantly if you take a wave.
Can take the engine home in the winter to service.
Prop stays in the water when it's rough.
Can easily clear a fouled prop.
Certain amount of steerage from the engine.
Outboard can still breathe (it's not in a locker)
Some battery charging from engine
Easier to work on if it breaks down than a transom mounted engine whilst at sea.

The disadvantages are:

Difficult to lift the engine out completely when racing. Leaving it in (particularly in light winds) causes drag from the prop, even if it is left to spin.
Can get fumes if there is a following wind.
Can be noisy (less so with 4-stroke)

You can lift the outboard out completely and fit a plug in the well to streamline the bottom of the boat when racing, but if you have an 8HP or 10Hp 4-stroke outboard then it is very awkward and heavy. I don't usually bother!.


https://flic.kr/p/XmvokN
Inboard Diesel


The inboard diesel with a folding prop is probably the most desirable option. Due to the age of the boats, most have had the original BMW D7 or D12 single cylinder engines replaced by now. A good replacement option is the Beta Marine 12hp. 7Hp is a bit underpowered for the Evolution.

The advantages of an inboard diesel are:

Reliability
Simplicity
Better for cruising
Good battery charging
Very little drag with a folding prop

The disadvantages are:

Folding prop is unprotected and sticks in the mud when drying out.
Prone to damage to prop or P bracket

For me, the outboard in the well is fine as the boat dries out regularly. I would say however that if you don't need to dry the boat out then the inboard diesel with a folding prop is a better proposition. Many of the Evolutions that originally had either an outboard on the transom or in a well have since been converted to inboard diesel.

by David Lincoln
Jolly Roger
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