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Message board > Navigation & sea worthiness > Sea Performance Trial for Hardy Bosun 20

Message 15 of 15
Posted by member Michael Herridge on Tuesday 1 June 2021

In theory yes but the pump is hard to hear when the engine is at high revs which it needs to be to plane. I will give it a try, thanks.

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Message 14 of 15
Posted by member Gary on Monday 31 May 2021

Can you not just switch them and count how many seconds they take to fully move then judge their position from time ? They should generally be fully down on opening the throttle and up when planing

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Message 13 of 15
Posted by member Michael Herridge on Monday 31 May 2021

* Aged Pilot with Bennet tabs. 50hp is not really enough for serious planing but it is possible. For me the only problem is that I have no way of knowing how the tabs are set apart from feel and using one's eyes as they pre date position indicators. I have been known to stop and have a look!

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Message 12 of 15
Posted by member Gary on Wednesday 26 May 2021

Richard, not sure if you realised, mine is a Navigator. Sounds like the hull profiles are quite different.

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Message 11 of 15
Posted by member Richard Jonathan Talbot on Wednesday 26 May 2021

Many thanks Gary. This is weird as my Bosun ( 4051 ) built in '02 has a distinctive recess all the way down on the transom to which the engine is bolted. This only gives me about six inches of flat surface on the quarters to which to attach any tabs. I shall have to scratch my head for a solution !

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Message 10 of 15
Posted by member Gary on Wednesday 26 May 2021

* Thats a clearer photo!

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Message 9 of 15
Posted by member Gary on Tuesday 25 May 2021

* I had to fit longer legs to keep the ladder further off the back and clear if folded down.

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Message 8 of 15
Posted by member Gary on Tuesday 25 May 2021

* Richard, a couple of photos. Adverts give various size options and plenty videos online as well as good instructions on fitting.

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Message 7 of 15
Posted by member Richard Jonathan Talbot on Tuesday 25 May 2021

An excellent series of posts. I too find my Bosun very weight sensitive. Gary, which size Nauticus tabs did you use to fit on the flat transom quarters ? They don't appear to give dimensions and we don't have a lot of suitable space to play with.

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Message 6 of 15
Posted by member Gary on Monday 24 May 2021

I'd highly recommend nauticus smart trim tabs Tony, not expensive and seem to do what they claim to. Push the bow down on acceleration so quickly get you on the plane then allow you to trim up/out for more speed or back off for maximum economy. I don't have a working tacho but can pull back to about 3/4 wot and stay comfortably on the plane.
Too early yet to give accurate fuel consumption but I'll follow your lead with a more detailed report in due course and update the performance file.

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Message 5 of 15
Posted by member Tony Knight on Monday 24 May 2021

Odd I know since it is, as you say Gary, the reverse of what one expect but it works with the set up on this boat ....which I did not do! The economy and ride suggests that it is working out OK and there is no bow steer. With the leg out some more, once on the plane, the bows reared up with a tendency to porpoise.

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Message 4 of 15
Posted by member Tony Knight on Monday 24 May 2021

I had the leg set straight down when powering up. This gave enough lift to the bow without it getting too high and obscuring vision but enough to help it up onto the plane within about a 150 metres. Trimming it in lifted the stern and pushed the bow down. There is a noticeable difference in the ride feeling, like the boat is riding on a cushion and one can then back off the revs whilst still remaining on the plane. I guess the amount of trim required at the start, and the extent to which one trims in once up, is very much dependant upon the weight in the stern and aft section of the boat. In my case, as well as the heavy engine I have a battery, 2 x 25 litres of fuel, 4 litres of oil, warps, bilge pump and a gas bottle: all right aft.

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Message 3 of 15
Posted by member Keith Lathwell on Monday 24 May 2021

Great post Tony, your consumption matches matches closely my own. My Bosun has a Honda 75hp engine but I am using a 4 bladed 13 1/4" X 13"p prop.

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Message 2 of 15
Posted by member Gary on Sunday 23 May 2021

An interesting report with the details we need, pretty good mpg too. You say you trimmed fully in once on the plane , how was she trimmed before you opened up ? I always thought you opened up with it trimmed fully down ie in, then trimmed up a bit once on the plane allowing you to reduce the revs.

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Message 1 of 15
Posted by member Tony Knight on Sunday 23 May 2021

There is not too much performance data, and the supporting conditions around for a Hardy Bosun so I thought I would share mine.

I was finally able to conduct a sea performance trial for my recently acquired 2000 Hardy Bosun 20. She has a 75hp Mariner Optimax, fitted in 2015 which has 150 hrs on the clock. The prop is three bladed 13.75 dia 15" pitch original. The boat had a clean hull, was carrying 50 litres of fuel, 5 litres of water and there were three people on board weighing approx. 250 kg in total, in addition to the usual gear. The engine maxed out at 5200 rpm giving 22.5 knots in a calm to moderate sea with 10 knots of wind. She tracked straight with hands off of the wheel. She came up on the plane at around 14 knots. With the leg trimmed fully in she flatted out for a comfortable "cushioned" ride at around 16 knots and one could back off of the revs down to 4150.

She was able to execute 180 degree gentle turn maintaining planning. The stability is greatly affected by weight distribution. With "roll tacking" at slower speeds with a shift of weight to the gunwales to drop the fenders. Balancing the weight in the wheel house both bringing it forward from the stern and putting the heaviest midships improved performance and permitted progress at lower revs.

She slammed going through chop/wake at right angles but was far happier rolling across it broadside to. In both cases she fell off of the plane and needed to be accelerated to restore planning. Across 23 nM of mixed running averaging around 14knots overall she burnt through 20 litres of petrol achieving 1.15 nM per litre. Most of the time was spent cruising at 16 knots.

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