Mini-Motorboat "New Sargan"-modification with Rhino 5 and Orca3D

Hi friends of Boat Design.net,
I want to show you modification which I has made as much as possible coming nearer to data of offset table of the original version of motorboat "Sargan" published by D.A.Kurbatov in his book "15 designs of vessels for amateur construction ”, 1985.
For deriving the faired hull contours it was necessary to make small changes in some ordinates. In outcome the Breadth overall was received not much less / on 27mm/.
I have shown characteristics of the original boat.
The model which you now see has the following characteristics:
At total displacement D=250,71kg in a salt water on an even keel, displacement condition floating, the draft is T=0,216m.
In this condition / in departure- water-line of rest / data are the following:
Loa=2,7m; Boa=1,273m; Amidships depth/Х=1,35m from AP/-H middle=0,543m

Lwl=2,438m; Bwl=1,067m; Breadth on a bilge at transom- B chine=1,04m

Cb=0,435; Cwp=0,817; Cx=0,701
LCB=0,861m from AP; VCB=0,144m from BL
Deadrise of the bottom at transom = 17 deg as on the original.
On figures 1-4 and 13 you will see different images of the model.
On figs 5 you will see the Linesplan of the boat without the bilge spray wedge and without planing steps it is carried out on program Delftship Professional.
On figs 6 you will see the Linesplan of the finished model of the hull it is carried out on program Orca3D.
The Offset table you will see on figs 7.
On figures 8,9 and 10 you will see hydrostatic curves of the motorboat at a zero trim for different sizes of the draft up to 0,4m from BL.
On figs 11 are shown forecast sizes of the resistance, speed and power at the following input data:
LCG=LCB=0,861m from AP; VCG=0,35m from BL

The axis of the propeller of the suspended motor is accepted on Z = - 0,175m from BL;
Point of application of the thrust on the axis X = - 0,25m from AP;
Shaft Angle to BL =0 deg;
The minimal rate of speed15 km/h;
Maximum rate of speed 50 km/h;
Design speed 27 km/h;
Reserve at account of resistance =10 %
Propulsive Efficiency=50 %
Outcomes of account of speed/power:
At 27 km/h- N total=10,8hp; Running trim=6,948 deg; Volumetric Froude Frv=3,029
At 50 km/h- N total=22,2hp; Running trim=2,927 deg; Volumetric Froude Frv=5,609

And at two speeds forecast Orca3D gives ОК.
On figs 12 it is shown the schedule of the running trim angle of the motorboat.
On figs 11 it is visible that the smallest resistance R bare=458,8 N is received at speed 34 km/h and
N total=12,8 hp; Trim = 5,04 deg; Volumetric Froude Frv=3,814
If the Volumetric Froude number is => 3, it means that the motorboat enters in a condition of planing.
Accounts on speed and power show more acceptable longitudinal stability at speed 45-50 km/h.

 

Mini-Motorboat "New Sargan"-modification with Rhino5 and Orca3D-continue

What we will be necessary to know for reliance that this motorboat will planing?
1. For the first time, that which to decide her to make it is necessary to receive the mass of the hull<=65kg, irrespective of the chosen material.
The original alternative is made in composite modification - wood set as a former, sheathed by a thin glass fibre laminate then pasted over woven fiber glass.
But meaning major progress in the production technique of plastic yachts, bodily the plastic alternative likely will be preferred. It means a new construction plan and new units, different from published in the book.
2. The total displacement of the boat made by the following items:
- Hull with equipment /seats, glass, steering wheel/
- Suspended motor
- Supply - scull, life-saving jackets, etc.
- Fuel and oil in fuel cans
- Drink water, provisions
- Passenger / up to 2 persons / with baggage

It is not necessary to exceed 250 kg /as in the original version /.
Otherwise there is a high probability that boat is not planing, and to float only in displacement or a pre-planing regime. Then the output is only one - instead of two persons onboard will be only one passenger - motor-man. It in the greater degree depends on assignment of a boat.

Provisional decomposition of total displacement / in kg/:
- Hull… … … … … … …....... 60
- Suspended motor …..... 27 /12 hp/
- Passengers … … … …....150 /2 persons/
- Supply and store
/minimum / … … … ……..13 /fuel, drink water, life-saving jackets/
In total … … … … … … …= 250 kg

Decomposition of total displacement / in kg / at one motor-man:
- Hull........................... ………….60
- Suspended motor …..... ………44 /23 hp/
- Motor-man with baggage... 100 /1 person /
- Fuel, drink water, provisions,
Supply.................... ……………46
In total … … … … … … …..... = 250 kg

3. Accepted by me forecast primal sizes for LCG and VCG are subject to improvement after acceptance of concrete sizes about self-sufficiency in day or an endurance - distance up to the following item of a fueling, a sort and an engine power, speed which we want to reach and a navigation area. And certainly after modification of the construction plan.
4. It is possible to test the limit inferior of speed for the output of the boat on a condition of planing under the rough formula, specified in Kurbatov book:
v = 34*D 1/6 km/h
Where D - total displacement in /t/ or v = 34*0,25 1/6 km/h=26,98 km/h≈27 km/h

5. In this quick reference there is one more approximated estimation:
It is possible to consider, that the boat planing only in case on each kW an available power of the engine will have no more than 34 kg from the total weight of the boat /or 25 kg/hp/.
Let's make check for two speeds:
- For 27 km/h the engine power 12 hp is selectable
Then 250/12 = 20,83 kg/hp <25 kg/hp
That is means the boat will planing.
- For 50 km/h the engine power 23 hp is selectable
Or 250/23=10,87 kg/hp <25 kg/hp
That is means the boat will planing too.

 

Mini-Motorboat "New Sargan"-modification with Rhino5 and Orca3D-continue

Problems which the designer still should be clarified:
1. Whether this boat has stability and whether the freeboard is sufficient?
That is means how much there will be the actual initial metacentric height, up to what heights of waves the boat can float and on what pressure and a wind speed can sustain.
At an expected band of size for VCG=0,35m and VCG=0,4m at draft T=0,216m it is received:
GMt=BMt + VCB - VCG = 0,611+0,144-0,35=0,405m;
GMt=0,611+0,144-0,4=0,355m
That is GMt =/0,355-0,405/m
Size GMt is subject to ultimate improvement after experimental heeling test of the ready motorboat.
2. How to supply unsinkability of the motorboat?
But these problems are decided on the following design stage. The purpose of the present publication was to show you only as in 1985 people did absolutely quite good mini-boats.
For those which it is good use Russian I enclose the file of translation of the text part in Russian.
_______________________________
NA Razmik Baharyan

 

Hi, look's nice, but I am not sure about position of the longitudional redans at hull bottom. They will works better if you place them along watrlines.

 

Hi Alex,
I enclose the file of the body line of the original boat.
Arrangement of the planing steps /redans/ is linked with the breadth of the planing plate of the bottom.
At a total load 250 kg the boat glides between the planing steps which are on the short-range to the bilge.
There is also a case when the boat glides at breadth of the gliding plate 340mm limited to the first planing steps from keel - at a diminished loads /one person / or enlarged up to 20 hp capacity of a motor.
I have not changed arrangement of the planing steps as the boat after the construction has been tested and has shown good seagoing capacities. It agrees with the author at 23 hp the speed of the boat will be from above 45 km/h.
__________________________
NA Razmik Baharyan

 

Hi Alex,
Basically your note is exact. I have seen „ Guide on motorboats, boats and engines “-1982, under edition of Novak G.M. There the arrangement of planing steps is specified as you write - see the file. But all the same I think that the most exact solution for their arrangement depends on test in actual operational condition or by means of model tests. Certainly the cheapest version is to trust in the original.
_____________________________
NA Razmik Baharyan

 

Generally they should be located to cross stream lines with maximum angle. And it should be perform after model test.

 

Hi All,
You look at the photo the proof for arrangement of the longitudinal planing steps/redans/ of the planing motorboat in planes parallel CL. The motorboat is built in UK.
______________________
NA Razmik Baharyan

 

I don't think you can make the hull/deck/interior at 60kg. Also, 13kg including fuel is way too low. If you carry enough for an hour, say 10l, it will weigh about 7.4kg.

 

Hi gonzo,
The hull of the original boat weight 65kg. He intended for two person.
If any one will decide to make such mini- boat it is necessary to have in view of limitation for total displacement 250kg, differently will not glide. And if to put more powerful motor or the hull will be received above 65kg then likely the boat will be maintained only by one person.
_______________________
NA Razmik Baharyan