Selway Fisher Harrier 9' 6" dory and Silver Century?

[Scorrie]

Hello folks, my first post on here (but I've been around SOS for a couple of years now).

I've got my trusty Silver Century long shaft sat waiting quietly in the byre for a new boat to perch on since we moved to Shetland. I'm thinking about building the Selway Fisher 9'6" Little Harrier dory, as I want a boat small enough to haul out of the water into it's traditional (but rather steep) 'noost' in rough weather and be car-toppable.

The Little Harrier is rated for o/b's up to 20hp and is said to give 20kts with a 10hp, I'm wondering what I'd get with the SC strapped to the back? I'm not bothered about speed at all (the boat would just be used in the bay below my house and on any suitable sheltered inlet for pottering about in), but would be interested to hear of anyone's experiences with a similar setup.

http://www.selway-fisher.com/Mcup16.htm#RIER

The SC was previously used on a heavily built and beamy 13ft glassibre working/rowing boat (it took six of us to lift it onto it's trailer....) that was built by McCaugheys of Wick, which it would push out into a sea at a fair old pace - so the weight difference will be massive on this one and it's a flat hull as well.

Anyone got an opinion on likely speed?

[NeilF]

Would a long shaft not be too long for that boat?

[Scorrie]

Probably, I reckon I'll be building the dory with a removable transom plate so I can experiment to get the height right without butchering the original transom if I get it wrong.

If I was still in Caithness, then I'd probably just pick up a standard shaft model from somewhere...but up here I'll have to make do with what I've got.

[blue]

hi scorrie---for displacement speeds you are dependant on the length of the boat at the waterline----so 9 feet at the waterline will be slow---there is a formula you can google ----or pm horsley-anarak who is a keen boat builder for advice-----regards blue

[Scorrie]

Hi Blue.

Yup, the formula is 1.34 x LWL x 0.5 IIRC, but that is for displacement hulls whereas this little dory is almost flat bottomed (just a slight 'V') - so I'd expect a little more speed from the boat. The question is how much (if any) more it would be as I have no experience with small outboards on planing/semi planing hulls.

If you click on the linky in my original post, it gives the dimensions and power the designer has come up with, 10hp = 20kts....but I'm not sure that will equate to a (theoretically speaking) 5hp = 10kts.

And I believe that 4-5hp is being a bit optimistic with a SC!

[Charles uk]

What your failing to add into your calculation is the loading.

With a 350 kilo load including hull weight it would be a very healthy 20 hp outboard that would pull this hull out of the water onto the plane, but you might do it with a Seagull & a five year old lightweight child.

I'd guess around 5mph maybe a little more if the hull is not a real heavy one with 1 normal weight adult!

[Scorrie]

I'll start dieting now

[JERSEYMAN]

funny thing Seagulls, I've got a 12' dinghy I run my Seagulls on and it does not seem to matter which motor I put on (40+, century, silver century plus, 102) the speeds seems to be the same 5 mph-ish, I haven't tried a Marston on it yet though

Don't expect too much speed unless you run a whippy 170

[Rob Ripley]

Here's a vid of my 14'clinker running with a40+

http://www.youtube.com/watch?v=_Kn3zXmp ... e=youtu.be

[Taspiper]

Here's a vid of my 14'clinker running with a40+

seems to get along nicely!