Outboard size for 4+2 cruising?

[Mdr24uk]

Hi there, new joiner looking at a Shetland Family 4+2 this afternoon which has a Mariner 60hp 4 stroke outboard.
I‘ve also been looking at another with a Penta 150hp inboard, and I’m concerned that this smaller outboard might be a bit underpowered for a 4+2?
The boat is for family days out estuary/coastal cruising around the Solent area.
Any thoughts? Today’s boat is already towards the top end of my budget, so having to buy a bigger outboard might be an issue.

Thanks in advance,
Mark

[dellquay13]

Hi,
It's only a metre longer than my F4, but at 1100kg nearly twice the weight. 60hp won't get it up on the plane very easily, but as Shetland describe is as a semi displacement hull and rated at 90hp max outboard, is it ever meant to go fast? Won't it play havoc with the chintz curtains and china crockery, crashing over the top of a westerly swell?
Chris

[ShipShape]

I have a 4 Plus 2 with a 30hp Mariner 4 stroke. Maximum speed is 8mph at just under 5000rpm, cruises nicely at 6mph at just over 3000rpm. Perfect for inland cruising but not for coastal. I would think 60hp should give you 15-20mph so probably the bottom end of whats needed for coastal but should be OK. As previously said, although it is only 21 foot, it is a heavy boat especially when fully loaded with passengers

[ladydawn]

I’ve got a 4+2 with a 75 hip Honda and it’s fine for pottering about on the Norfolk broads but gives it a max top speed of 22 mph but it struggles to get there with two heavy adults , a dog a a weeks worth of fuel and other tat !

[Mdr24uk]

Thanks for the responses so far. I think I am going to need a bit more grunt!
I collected it from Southampton with a passage plan estimating 10kts, which turned out to be rather optimistic.
She maxed out at 6kts in the estuary, and once out on the open water we struggled against the tidal flow and crawled along to Pompey at around 3.5kts...
That was a long, bumpy journey with a 1m swell!

[dellquay13]

Do you have a tacho to tell you the max rpm you get? 6mph flat out is poor, and could be down to the prop being too coarse and the engine struggling to get to its best power band. You should get about 5500rpm with wide open throttle if the prop is right. If the engine previously came from a lighter boat, the prop will be too coarse pitch to get up to full rpm on your boat and changing prop for a lower pitch might help. Every inch of pitch you drop usually raises your rpm by about 200

[Clive]

Props are everything! Mine has an original Honda 35hp but we are on the River Wey or the Thames. I replaced my prop for a more suitable river use one (low speed, low revs). That said, with no boat history, I would be very surprised if it had not done coastal work as it has NASA equipment and shortwave radio. Maybe just Poole Harbour!

[Adam]

.... You should get about 5500rpm with wide open throttle if the prop is right...

Chris, I just wonder my prop is the right size. I have same boat as yours and same outboard power - can you just tell me what's your prop size? I can barely get 4500 rpm with full throttle. It goes on plane OK but I think it should be a bit better. The boat is quite fast - I can easily get 25-30 knots on flat water. On plane it does 15-17 knots at 3500 rpm depends on wind and water condition obviously.
My prop size is 13.25 x 17 and I have a feeling that the pitch isn't right.
Thanks, Adam

[dellquay13]

Hi Adam,

Strangely enough I looked at my prop today. It's 13 5/8 x 13 and I get 5800rpm and 27mph on a flat calm. I do carry a lot of weight though, fuel and food for a few days, tender and luggage for two.
Chris

[dellquay13]

Hi Adam,

With less weight I would expect to get a few more mph, but I'm more interested in fuel economy than speed. I try to cruise at about 4500 which is usually 17-19mph, below 4400rpm I tend to fall off the plane. My tacho is my most important engine dial, and as crucial as my plotter and sounder.
Chris