Core Sound 17 as a motor skiff

[Chespearl]

I know this will seem heretical to some, but I use my CS17 at least part time as a motor skiff and fishing vessel, motoring it in the local river without the rig, using a Honda 2hp air-cooled motor. I'd like to find something faster and quieter. Has anyone put a larger, heavier motor on a rig-less CS17?  5 hp, 8 hp, 10 hp? My open transom CS17 is well-built to the plans. During the build I added some stout quarter knees in the corners under the side decks. I'd like to mount the larger motor on centerline, directly on the transom, no rudder, steering the outboard with a PVC pipe tiller extension. I know a 5 hp Honda weighs ~ 60 lbs. Would that give me 10 kts with two people, 3 gallons of gas and fishing gear? Any experience or lessons learned would be appreciated.

 

I really don't want another boat just for fishing and I'm not looking for or expecting perfection, just something that works and is reasonably safe and stable @ 10 kts in typical river/bay conditions.

Thanks,

Brian

[PadrePoint]

I bought a 5hp Honda for my CS17m3 (Avocet). I place it on a bracket that extends about 10 inches past the transom. 
I’ve not used full throttle in it and have mostly brought it to about hull speed or maybe 5-7 mph. The noise is a little less “irritating” than my 2.3 hp Honda.  The transom bracket is square to the transom and isn’t a good angle, tilting up too much… I can’t modify the bracket. 
Next time I use my CS17 I shall try to remember to test these things… actual speed and some effects of weight distribution in the boat (I normally sit in the back of the boat when motoring, which is likely inefficient in terms of speed.  (Since the weather is looking OK, perhaps I can do this tomorrow.)

[PadrePoint]

I was able to check out some speeds on my CS17 with my Honda 5 hp motor. Nothing scientific here, just using my Navionics app with a few throttle levels. 

With the throttle at “start” position the app speedometer showed about 5+ mph. Increasing from “start” to half way to full moved the speed to just over 7 mph.  There wasn’t much more speed increase when when I went all the way to full throttle… reaching about 8 or so mph.  But, that is sufficient for me to get away from or back to a dock.  I’d think it would be enough to get to a fishing spot on a lake. 
 

As mentioned, I mount my motor on the bracket that came on the boat.  The motor is angled back from vertical and the prop is just low enough in the water (it works well enough for my purposes.)  I would think that a better motor placement would improve performance somewhat.  My boat might be a little heavier than yours since it is the version with a cabin.  And, as mentioned, the 5 hp motor has a more comfortable sound to my ears than that of my 2.3 hp.

 

Hope this helps. 

[Chespearl]

PadrePoint,

Thank you. That is helpful information. I'd guess that my boat is a 300 lbs lighter than yours, even more if you had the rig and rudder installed for your test. So maybe 400 lbs lighter for the fishing configuration I'm considering if i'm by myself. Sounds like 5 hp won't get your boat above displacement speeds, but I still wonder if it would work for me. 

 

Anybody else have any experience with this?

 

[Designer]

I think that it is good idea to use your CS17 as a motor boat. We used my BRS15 a lot with a 6 hp motor without rudder and rig. With 3 adults, 2 large dogs and picnic gear she ran at 7 knots. Running solo and trimmed out it seemed a lot faster. We did not have Navionics then, It was generally hard to find an accurate measured distance on the spur of the moment.

 

As best as I can calculate for your boat using a 10 hp motor. @ 600 # all up weight I get 10.3 knots and @ 1000# 8.9 knots. 

 

Take this for what it is worth because this is operating at hump speed and calculations can be way off. The ideal way would be to try and borrow a motor for a trial run.

[Chespearl]

Graham,

Thank you for sharing your experience and doing the calculations. Your numbers tell me 10 kts may not be a reasonable expectation even with a 90-100 lb motor. Maybe life at 6-8 kts is just fine too. Borrowing some motors for testing is a good idea.  If I come up with anything worth reporting I will share it on the forum.

 

Brian

 

[Don Silsbe]

Heres my fishing setup for my Bay River Skiff.  I use my 2.5 hp Suzuki.  I’d love to test out a 9.9…