HP requirement?

[Condi]

What is the minimum HP requirement for a small (16ft) fishing/cruising vessel to go to sea? Obviously will depend on sea condition, wind etc, but generally speaking? At the moment it has 5hp 4 stroke which will do about 4 or 5mph on still, inshore water, and I believe it used to go to sea quite comfortably with the same engine, but something makes me a little nervous without a little more juice.

Any comments from the floor?

The boat is a SeaSafe Dandy which seems to get good comments regarding its inshore capability.

[NickCQ]

What’s the boat’s displacement? Do you get ventilation issues with the outboard (short shaft?)

Personally I’d rather have two 5hp than one 10hp in a motor boat for redundancy.

[Condi]

Displace is about 1 tonne I think.

Ventilation issues? Hmmmm, not that I know of.

[paintman]

I believe the Seasafe Dandy is a displacement hull so you will be limited to a maximum speed by the boat's length (waterline) regardless of how big the engine is.
I'd suggest you try & find the original manufacturer's spec as this will give recommended engine size range.

Edited by paintman on Friday 6th July 20:04

[Condi]

Yes, definitely a displacement hull.

[paintman]

May well be a plate on the boat with manufacturer's recommendations.
As I said earlier a displacement hull is limited in max speed regardless of engine size. Calculated against the length at the waterline. Many calculators available, this is a random example:
https://www.easycalculation.com/physics/classical-...

Also note that you will need to be aware of the tide & tidal runs as you may find yourself trying to go against flow that is equal to or exceeds your boat's speed. A place I go to in Cornwall used to have a number of small hire boats & the hirers were told by the owner not to go beyond a certain headland. If one of them hadn't returned by early evening we knew exactly where they'd be, off the headland flat out against the outgoing tide going nowhere. An easy recovery but you could get in a mess with your own boat.

BUT don't get too wound up as I - & several friends - used small 12 foot-ish boats with small outboards in the same area in the early 70s without issue. Most were clinker built with small Seagulls, mine was 12' GRP with a 4hp Johnson twin cylinder 2-stroke.

Edited by paintman on Saturday 7th July 20:14

[Slushbox]

Displacement hull - long keel. Was about 1000Kg all up, I think.

They tended to be fitted with 5-8HP outboards. As mentioned, displacement hull means no planing, so they would usually be propped for torque at medium range rpm.

I'm out of touch with the latest breeds of outboard, but had a Mariner 8HP on a similar boat which was perfect. There are sailing specific outboards like the Tohatsu Sail Pro. 8HP O/Bs also tend to have battery charging outputs and twin cylinders.

It looks like the boat needs a long-shaft from the pics, but you would need to double check transom height.

[Condi]

Thanks. It seems like my 5hp single cylinder Mariner is already getting about max speed out the hull, so while some more horses would be nice, spending £800 or more to get 3hp more doesnt seem very sensible.