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Old 05 September 2016, 05:01   #1
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Country: UK - England
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Boat name: Alexis
Make: White Shark
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Aerotec performance and transom splash variations

Good morning !

Second outing with the Aerotec this weekend, which I purchased largely off the back of recommendations on this forum, so thank you ! It's a fantastic bit of kit, well made and almost uncannily stable in a chop, with very surprising grip levels in tight turns.

I had a couple of questions for the more experienced Aerotec users on the forum, which a bit of searching hint at the answer to but not definitively:

(1) Performance: I have a new Mercury 4-stroke 20hp to match to the boat. It's now just about fully run in after the long first outing and at the top of the tide and in a very light chop (maybe force 3) I got a two-way average of 21 knots at WOT. I'll confess I don't know the prop dimensions but it is whatever comes as standard [update: a bit of research suggests it is a 10 pitch prop]. This was one up with one kit bag of safety items and food/water, full tank of fuel and small anchor and chain. So let's say conservatively a 150kg load. Does this seem right ? I'll confess I was expecting more like 25/26 knots so was slightly disappointed, though to be fair the motor is extremely grunty low down and pops it up on the plane almost instantly so I'm very happy with it. Much smoother than the two strokes I used to run years ago. I didn't want to go for the 25hp at that isn't really man-portable, whereas the 20hp is (just about) at 48kg.

(2) Splash variation: I have read lots of posts about the transom splash issue, so when I took it for its first outing I was very surprised to have almost none ! This was with the Mercury on setting 2 of the 5 trim positions (1 being trimmed in, 5 being trimmed out) and two big blokes and the aforementioned safety kit, so let's say a 250kg load. Contrast that with the second outing, and I was drenched !! Do people generally experience big variations in splash with different loads ? Trimming the Mercury out one to position 3 did help significantly, though it is not an ideal solution as then the boat rears more to get on the plane (though it is fine when it is up).

Very grateful for thoughts and feedback. Here's a gratuitous photo !
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Old 05 September 2016, 05:17   #2
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Country: UK - England
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21knots sounds about right to me, I have achieved just shy of 20knts, 1 up, with a lighter 2stroke 15hp.

Yes, the loading in the boat makes a big difference to the transom splash. As long as the water doesn't get inside the boat I just live with it. Splashier when the boat is running lighter.

Enjoy the boat, they are lovely bits of kit.

Simon

Quote:
Originally Posted by WhiteShark View Post
Good morning !

Second outing with the Aerotec this weekend, which I purchased largely off the back of recommendations on this forum, so thank you ! It's a fantastic bit of kit, well made and almost uncannily stable in a chop, with very surprising grip levels in tight turns.

I had a couple of questions for the more experienced Aerotec users on the forum, which a bit of searching hint at the answer to but not definitively:

(1) Performance: I have a new Mercury 4-stroke 20hp to match to the boat. It's now just about fully run in after the long first outing and at the top of the tide and in a very light chop (maybe force 3) I got a two-way average of 21 knots at WOT. I'll confess I don't know the prop dimensions but it is whatever comes as standard [update: a bit of research suggests it is a 10 pitch prop]. This was one up with one kit bag of safety items and food/water, full tank of fuel and small anchor and chain. So let's say conservatively a 150kg load. Does this seem right ? I'll confess I was expecting more like 25/26 knots so was slightly disappointed, though to be fair the motor is extremely grunty low down and pops it up on the plane almost instantly so I'm very happy with it. Much smoother than the two strokes I used to run years ago. I didn't want to go for the 25hp at that isn't really man-portable, whereas the 20hp is (just about) at 48kg.

(2) Splash variation: I have read lots of posts about the transom splash issue, so when I took it for its first outing I was very surprised to have almost none ! This was with the Mercury on setting 2 of the 5 trim positions (1 being trimmed in, 5 being trimmed out) and two big blokes and the aforementioned safety kit, so let's say a 250kg load. Contrast that with the second outing, and I was drenched !! Do people generally experience big variations in splash with different loads ? Trimming the Mercury out one to position 3 did help significantly, though it is not an ideal solution as then the boat rears more to get on the plane (though it is fine when it is up).

Very grateful for thoughts and feedback. Here's a gratuitous photo !
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Old 05 September 2016, 05:52   #3
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Country: UK - England
Town: East Anglia
Boat name: Nimrod II
Make: Aerotec 380
Length: 3m +
Engine: Suzuki DF20 EFI
Join Date: Nov 2007
Posts: 2,535
Shiny new one eh?

Anyway as Simon replies... yes and yes.

Re speed you are about the same as my 20hp Suzuki which has not masively raised the top speed over my previous 15hp Mariner 2-stroke but has greatly improved the jump onto the plane and the ability to work the waves on/off plane in rough weather.

I run a 10" prop by choice but have a 11" spare and this makes no great difference to speed one up... and bogs it down loaded.

If you want 26kts from a 20hp you need a light hard hull RIB.

Yep splash changes according to outboard model, loading, trim and wave state. Thankfully my Suzuki has a far lower splash than the old Mercury but with a wrong combination of circumstances can still give the odd spray over the transom.
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Old 05 September 2016, 05:59   #4
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Country: UK - England
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Boat name: Alexis
Make: White Shark
Length: 6m +
Engine: Yamaha Offshore 300
Join Date: Apr 2016
Posts: 14
Thanks both, this is very interesting feedback. So 11" pitch is not the way to go then ? I thought that would probably get me a knot or two but if it will struggle loaded (say, 4-up) then clearly not a good idea.
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Old 05 September 2016, 06:14   #5
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Country: UK - England
Town: East Anglia
Boat name: Nimrod II
Make: Aerotec 380
Length: 3m +
Engine: Suzuki DF20 EFI
Join Date: Nov 2007
Posts: 2,535
I have a Tinytach type rev counter and with a load the outfit feels less lively and refuses to pull anywhere near max revs on an 11".

Don't be disappointed by the speed though. We all have different priorities and they don't suit everyone but for our use and our load the Aerotec enables better progress in difficult conditions than any of the previous six SIBs we've owned.
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Old 05 September 2016, 06:18   #6
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Country: UK - England
Town: London
Boat name: Alexis
Make: White Shark
Length: 6m +
Engine: Yamaha Offshore 300
Join Date: Apr 2016
Posts: 14
Really useful to know, thank you.


I guess "disappointed" was incorrect word choice; I'm actually delighted with the overall performance taking into account all variables (your choice of the word "lively" is bang on the money) and frankly top speed isn't that important as one of the reasons for getting the boat was to entertain the children with towed inflatables etc, so 'hole shot' (as I think the Americans call it) is actually much more important.


I think tinkering with set up and exploring the variables is half the fun with these things sometimes !
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