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Lotus

An other OC20 build !!

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14 hours ago, Riggs said:

Looking very good Lotus. I do like that radar arch in the fact that it comes down nice and simple like.

Thanks Riggs. now complete with anchor and navigation lights !

 

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Finally the great day has arrived  . The highly modified Ocracoke 20  named Elusive 20 hit the water for the very first time !

My first impression is that she is a little bit bow heavy , by the way she sits on the water . All the rest is superb !! 

If I shift the 2 battery backward  and put the auxiliary motor of about 50kg  ( that is still unavailable ) at transom she might be leveled correctly. At the moment the batteries are located inside the cabin under the 2 steps to step inside.

 

Some performances data are as following in choppy water of about 1 to 1.5 "  waves.

 

800 rpm ( idling)  2-3 knots

2000 rpm   7 knots  and 6 liters per hour

3500 rpm   20 kts   and 17 l/hr

4000 rpm   24 kts   and 21 l/hr

and

6300 rpm   41 kts   and 70 l/hr in very calm water (47 miles !! ? )

 

I liked the best cruising speed of 21-22 knots ( 25 miles ) at around 3600 rpm . She cuts trough bigger chops like knife into butter with no splashes and slamming sounds and a very dry ride all thanks to Graham and his hull designs !  

The boat rides much more stable with the trim tabs slightly trimmed down at speeds of 18 kts and over. This may be because  of a heavier bow that can be addressed with a better weight distribution .

The propeller is a 16" diameter by 20"pitch attached to a Suzuki df200ap and think it is under propped  as the engine is revving up to 6300rpm that is its limit. May be a 21 or 22" will be much  better all over the rpm range . But don't know how this will effect the fuel efficiency !!

 

Over all I am very happy and satisfied with the results and the whole project !

 

Would like to say a big THANKS to Graham for all his help and patience answering my questions  ( a lot of questions !! ? )  and also all members in this forum that contributed with their comments !

 

THANKS again !

 

 

 

 

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Emvrin,

 

Congratulations!!! You outdid yourself this time. You put the rest of us to shame with the quality of your work. She looks beautiful. You do need a larger prop with 6300 rpm at wot. Have you weighed the boat?

 

Because the keel is straight and level as designed, if you can put a mark on the bow and maybe on the forward edge of the leg at the water line next time that you are in the water. You can measure down to a keel line extension back on land and we can calculate her weight and trim.

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Congrats Lotus - she looks amazing!  Elusive is a very fitting name..

You went to town with the 200hp ? - nice!

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5 hours ago, Designer said:

Emvrin,

 

Congratulations!!! You outdid yourself this time. You put the rest of us to shame with the quality of your work. She looks beautiful. You do need a larger prop with 6300 rpm at wot. Have you weighed the boat?

 

Because the keel is straight and level as designed, if you can put a mark on the bow and maybe on the forward edge of the leg at the water line next time that you are in the water. You can measure down to a keel line extension back on land and we can calculate her weight and trim.

 

Thanks a lot Graham, really appreciate !

 

I haven't weighed it but I know for sure that the floor ,sole ,is almost parallel with the sea water . I doped some water on the sole when no body was in the boat including me . The water remained stationary and after a while it moved slightly forward ( instead of backwards ) Therefor the self draining sole is not working ! At transom the water level is as the water line indicated on the plans. 

Again I still need to put the auxiliary motor and move the 2 battery to transom . Hope this will solve the problem . If not I can relocate one of the fuel tanks that are easily accessible .

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4 hours ago, lenm said:

Congrats Lotus - she looks amazing!  Elusive is a very fitting name..

You went to town with the 200hp ? - nice!

 

Thanks Lenm. 

You are doing a great job too ! Hard work pays off ?

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On 1/10/2020 at 8:28 PM, Designer said:

The cockpit sole is pitched aft 1 degree. That means that you are trimmed down by the bow a fraction over 1 degree.

 

1 degree in a waterline length of 15 feet is about 3" in height .  Think I have to shift a lot of weight to transom  to level !!

A 110 pounds auxiliary motor at transom and shifting  80 pounds batteries from under console to transom area would not be enough ?

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I checked the plans and the cockpit only slopes .8 of one degree. I trimmed the bow down from the stern WL .85  degree which gives you a bow down trim of 3" and a displacement of 2714#. It should take around 800 foot pounds to bring it to trim. Of course this is very rough as we do not have exact trim measurements. When I look at where the water meet the chine the boat shows it further forward than the trimmed down drawing. The boat could also be heeling slightly to the camera.

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Hi Graham , I managed to shift some weight backwards , batteries fuel tank and have installed the auxiliary motor. I have to see how she trim next time I put her in water . Waiting for some good weather. 

 

About the prop I was thinking of going to 4 blade prop instead of changing the pitch. At the moment I am running a 3x 16x 20" and goes over 6300 at wot. So either go for 3 bladed  16 x 21.5" or  16 x 23"  or the 4 bladed  15.25 x  20" or even  15.25 x 22" . These are the original suzuki props available .

I dont mind if I loose a couple of knots at the high end ( this is not a speed boat ) , I am looking for the very best cursing speed and fuel economy  at around 3500rpm,

 

An other question is , dose it make sens to go for a counter rotation prop, because the auxiliary motor is installed at port side and the boat leans slightly that side when no one on board . The ap series motor have the selective rotation control function so it is very easy to switch between , just change the prop and a plug in the harness.

 

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I would go with the 4 blade. There is no guarantee that it will be exactly the right size as it is still a bit of trial and error. Suzuki should have a lot of data on their props.

 

I see that the auxiliary is a right hand prop which means that it will tend to turn the boat to port but with the motor rigged th port will tend to turn the boat to starboard. Therefore the two forces are tending to cancel each out. The forces will vary with rpm but it is all moot as you have vectored thrust so you will automatically cancel it out with your wheel. It might have an effect when you start to move from a dead stop so it will be worth experimenting in an open space. 

 

I look forward to hearing the rest of the story.

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Now that the weight is shifted she floats perfectly , parallel with the original plans water line, but just a little deeper because of the overall added weight. ( sorry for no photos as we were in a hurry because of a bad weather ).

 

We have tested a 4 blade propeller 22" . It noticed that the response was immediately and with just a little acceleration the boat was on plane. The bad side of this prop is that it generates a lot of lift and the boat was very unstable at 30 knots and over .

 

This 4 blade prop also produced a lot of prop torque and the boat roll was very noticeable to the left side at acceleration.

I think that these 4 blade prop are at their best on heavy load boats with planing problems.

 

Fuel consumption also increased , but with a 22" prop the boat was over propped,  as wot was just 5400 and 36 knots.

At 3500 rpm she hit 18 knots and 19 liters per hour , way too worst than the 3 blade 20" 

 

Next time I will test the 4 blade 20", just for curiosity but think the perfect prop for this boat will be the 3 blade 21.5" prop. 

 

Will promise you some photos next time tested !

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35 minutes ago, Lotus said:

The bad side of this prop is that it generates a lot of lift and the boat was very unstable at 30 knots and over .

 

 

 

Are you sure the prop generates the lift and hence instability?  Or is it the speed of 30 kts and over?

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Hi Hirilonde, my first test was with a 3 blade 20" prop the boat was stable even at 40+ knots ! 

4 blades generate more lift and torque than 3 blade same pitch 

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Sounds like you are getting closer to optimum setup..

Look forward to some pics.

Is your self draining deck working better now?

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20 hours ago, lenm said:

Sounds like you are getting closer to optimum setup..

Look forward to some pics.

Is your self draining deck working better now?

 Thanks Lenm,

 

Yes the self draining deck is working perfectly. Well not exactly a self draining deck as I connected all drain pipes into a sump with an automatic bilge pump inside .  I could have made it self draining but my boat surveyor told me that the drain outlet should be at least 4" above water line , and that was impossible .

I had raised the whole sole by 2" from the original plans to compensate for the additional weight so it can be easily self draining by just adding 2 scupper valves.

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As promised here are some photos.

We have tested the 4 blade prop 20" pitch. It performed very similar to the 3 blade 20" but also generated lots of lift . WOT was 6050 rpm and 38 knots . Still think that best prop will be 3 blade 21.5" pitch. That will be her 4th and last test  

Best cruising speed was at 3600 rpm  22 knots  and 0.8 liters per knot mile .

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