Drag - with and without engine

On Sailnet there is a thread about a sailor who is going from an inboard (Atomic 4 in an Irwin 32) to an outboard. Along with the back and forth about convenience, powering ability in rough weather, and resale value this came up (see attachment). The claims made seem pretty unbelievable and I think are certainly exaggerated. But what does anybody else have to say about this? How much difference would losing an engine, shaft, strut and prop really make to performance?
Brian

 

not in a sailboat but in a 16 ft single engine power boat I was recently towed in by the coastguard.... I was supprised they wanted the dead outboard engine down during the tow....I was told that if they stopped during the tow my boat would also stop quicky and not keep going into the back of there boat .....so yes I can beleive that a simple prop and skeg produces a lot of drag .....

 

If he is racing the boat in relatively calm water then he may not regret the decision.

It might make the difference of 0.5kt in say 4 to 4.5kt range. Basically ghosting conditions. It could be more like 4 to 5 kts if the prop is 3-bladed with fixed blades.

Once the boat starts getting into heavy wave making then the prop is a lower proportion of the drag. For 32ft it could be 7.5kts with inboard rather than 8kts without.

A saildrive with folding prop does not add much drag. The extra weight over an outboard is not much once fuel considerations for range come into play.

An outboard can be next to useless in decent seas unless it is mounted through the hull rather than over the stern. Even then it will not match what you can get from an inboard.

The diesel will offer better range for fuel carried. There is the safety aspect of diesel versus an outboard as well. The venting of a gasoline tank needs to be done properly. Consideration should be given to a vented fuel tank location that does not allow fumes below. A small outboard is also close to useless for any electric power requirements - typically 1/4 of what a diesel will charge.

Rick W

 

"...lowered the center of gravity about 2 inches..."

i cannot believe that...
the engine is in most cases (do not know the Irwin 32 though) mounted very low in any sailing yacht... often below the waterline and always almost below the center of gravity...

how should the removal of one of the heaviest equipement which is already mounted below the center of gravity LOWER its center of gravitiy even further?
impossible and complete BS in my opinion...

 

You assumed right Brian!

Exaggerated and false. A real "expert".