FAQ FAQ  Forum Search   Events   Register Register  Login Login

New Boat project

Page  <1 234
Post Options Post Options   Likes (0) Likes(0)   Quote MATTOO Quote  Post ReplyReply Direct Link To This Post Posted: 03 Sep 2019 at 5:56pm
MATTOO View Drop Down
Titanium
Titanium


Joined: 10 Sep 2010
Location: The Dawn
Status: Offline
Points: 5250
Could be me.
I'll re read the post.
Thanks.
Just cruising in my now sweetas pimped out Southern 755 HT0!
Back to Top
Post Options Post Options   Likes (0) Likes(0)   Quote MATTOO Quote  Post ReplyReply Direct Link To This Post Posted: 03 Sep 2019 at 5:58pm
MATTOO View Drop Down
Titanium
Titanium


Joined: 10 Sep 2010
Location: The Dawn
Status: Offline
Points: 5250
Thanks Legacy,

Yes should of been directed to Steps.

However the principle is for us all.
Just cruising in my now sweetas pimped out Southern 755 HT0!
Back to Top
Post Options Post Options   Likes (0) Likes(0)   Quote Legacy Quote  Post ReplyReply Direct Link To This Post Posted: 03 Sep 2019 at 6:19pm
Legacy View Drop Down
Platinum
Platinum


Joined: 07 Aug 2010
Location: Huia
Status: Online
Points: 2244
If Steps boat is 5.5-6m , 9m of chain isn’t unreasonable (1.5xBoat length). Also weight of the anchor has some bearing on how much chain you’d want .
Back to Top
Post Options Post Options   Likes (0) Likes(0)   Quote Bounty Hunter Quote  Post ReplyReply Direct Link To This Post Posted: 03 Sep 2019 at 8:43pm
Bounty Hunter View Drop Down
Titanium
Titanium
Avatar

Joined: 14 Nov 2002
Status: Online
Points: 3762
Originally posted by MATTOO MATTOO wrote:

Mc Skipper,
Noticed your chain lengths and sizes.

May I suggest that if you have 9 metres in all its a bit more than you may need.

The principle with an anchor is the chain is the actual anchor.

Even a tanker works the same principle.

Although the anchor has a grab factor it's the length and weight of the chain that is actually the anchor.


I hope that gives you food for thought.

sorry Mattoo - this is incorrect and poor advice. 

the anchor is the anchor. its holding power is a factor of design, surface area, weight and the type of seabed its on.

the weight of chain and the catenary effect it creates does act as a dampener and it has an abrasive resistance that a nylon warp doesnt which is the thrust of your advice - but weather conditions can be sufficient to make the chain/warp scope bar straight and negate both of the above attributes.

Which is why you need an anchor 'sufficient' to your requirements.

It is best practice to put more weight in the anchor and use only 'minimum' chain. minimum will be a combination of required SWL and length for abrasion.

However, as you say - 9m of chain in this case is more than the usual smallcraft recommended amount of 1.5xboatlength
Death - Our community's #1 killer
Back to Top
Post Options Post Options   Likes (0) Likes(0)   Quote MacSkipper Quote  Post ReplyReply Direct Link To This Post Posted: 04 Sep 2019 at 6:15am
MacSkipper View Drop Down
Titanium
Titanium
Avatar

Joined: 04 Jul 2014
Location: Manukau Harbour
Status: Offline
Points: 3727
Thanks guys, Mattoo I have 6m of light chain and a danforth anchor, I also have a grapple if I know I am anchoring in a rocky area - got the danforth stuck once Embarrassed
 
In the Manukau tidal channels I use gps speed to tell me when anchor biting initially and line up on a few landmarks and check at first then occasionally - have ended up moving down the harbour before and don't want to go over the bar!
Good fishing trip nothing breaks, great trip catch fish.
Back to Top
Post Options Post Options   Likes (0) Likes(0)   Quote MATTOO Quote  Post ReplyReply Direct Link To This Post Posted: 04 Sep 2019 at 7:07am
MATTOO View Drop Down
Titanium
Titanium


Joined: 10 Sep 2010
Location: The Dawn
Status: Offline
Points: 5250
Thanks guys,
Always room for me to learn.
Just cruising in my now sweetas pimped out Southern 755 HT0!
Back to Top
Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 04 Sep 2019 at 8:23am
Steps View Drop Down
Titanium
Titanium


Joined: 14 Oct 2013
Location: Sth Auckland
Status: Offline
Points: 8593
If Steps boat is 5.5-6m , 9m of chain isn’t unreasonable (1.5xBoat length). Also weight of the anchor has some bearing on how much chain you’d want .

 Oh dear, the science of an anchor..
How does the anchor 'release' from the bottom when you pull it up?
As you remove the weight of the wrap and chain the arm lifts, as it lifts it levers the blade end up, and releases.
 And this is the 2nd most common reason for a anchor to drag.. not enough weight in the chain to hold the arm down in high currents/storm winds etc.
 Simple
Large ships often carry huge weights that slide down the anchor chains to add weight in storms, to prevent the arm lifting.

So why 3m 6mm, then 3mm 8mm, then 3mm 6mm come about?

The size of the anchor can be smaller... with more chain.. mine is smaller due to space between the anchor and the truck , and that it is a spare anchor  now permanent because lost the original some yrs back in rocks.

I did have 6m of 6mm which when went to the smaller anchor would occasionally drag when current and wind in the same direction. I had a spare 3m of 8mm laying around.
The 6mm is easier to 'tie' on the bollard.
And the hole between the hatch and deck is for 6mm..
When goes from rope to 8mm chain on the capstan would jam / tangle , which was rather dangerous for someone inexperienced and not expect that.
Which meant putting the 8mm in the middle.

And the 1st most common reason a anchor drags is being dropped too fast and the chain passes the anchor, tangles preventing the blades to lay well.

you would be surprised just how small an anchor you need for a boat with more chain to hold the anchor arm downWink

Then there is my 'bungy cord anchor, to enable mooring close to rocks in side winds / swells / current changes in upto 5/10m water.
Drop the bow anchor, reverse up 20 odd meters past where want to moor. Drop the bungy anchor,
Pull up manually on the bow anchor till bungy cord is a good 75/80% stretch and rear anchor holding well. Thumbs Up

Back to Top
Post Options Post Options   Likes (0) Likes(0)   Quote MacSkipper Quote  Post ReplyReply Direct Link To This Post Posted: 15 Sep 2019 at 9:58am
MacSkipper View Drop Down
Titanium
Titanium
Avatar

Joined: 04 Jul 2014
Location: Manukau Harbour
Status: Offline
Points: 3727
Finally received bushes and fitted for outboard trailer lock - removed as rusty and stiff -


Received new bushes cleaned up bracket and treated with POR 15 -


Finished and on outboard looks neat and moves easily - applied Inox all over and wont use WD 40 as swells plastic bushes.




Good fishing trip nothing breaks, great trip catch fish.
Back to Top
Post Options Post Options   Likes (0) Likes(0)   Quote MacSkipper Quote  Post ReplyReply Direct Link To This Post Posted: 08 Oct 2019 at 12:58pm
MacSkipper View Drop Down
Titanium
Titanium
Avatar

Joined: 04 Jul 2014
Location: Manukau Harbour
Status: Offline
Points: 3727
Got out lovely conditions though fishing pretty hard - with 2 people 30L fuel and fishing gear -

3500  27km/hr
4000 33km/hr
4500 38km/hr
5000 45km/hr
5200 47km/hr WOT

WOT range (service manual) 5000-5700

Was out in rough conditions a while back on my own - 
1 passenger (2 is normal loader 4 heavily loaded) hit 51km/hr at 5600 rpm

2 onboard old prop 44km/hr 4850 WOT  (with new prop holeshot really good runs a lot "smoother" and revs out now when you drop the throttle almost laboured before)

Hull 170kg motor incl battery approx 100kg 40hp   4.4m long tinny

Prop supplier thought motor was a bit low - can go up a notch will check when I get motor serviced what mechanic thinks I feel it is ok
Good fishing trip nothing breaks, great trip catch fish.
Back to Top
Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 08 Oct 2019 at 1:53pm
Steps View Drop Down
Titanium
Titanium


Joined: 14 Oct 2013
Location: Sth Auckland
Status: Offline
Points: 8593
It is a Ratio 1.83 gearbox ratio right?
40hp 2 or 4 stroke?
4.4m hull
WoT range 5000-5700

3500  27km/hr   (16.8 mph)
4000 33km/hr     (20.5mph)
4500 38km/hr     (23.6 )
5000 45km/hr     (28 )
5200 47km/hr WOT  (29.2 mph)

Prop pitch and diameter ? needed

Sry need to keep data all together otherwise have to spend ages going thru back posts / pages digging info out
Back to Top
Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 08 Oct 2019 at 2:33pm
Steps View Drop Down
Titanium
Titanium


Joined: 14 Oct 2013
Location: Sth Auckland
Status: Offline
Points: 8593
Tentative calcs. based on above.. assuming, IF have a 11.5" pitch prop and 1.83:1 gearbox
You are smack on right with slip numbers @ WoT and 4000 rpm cruise with that prop.Thumbs Up

If engine height is correct the theoretical weight calculated from WoT top speed will be in ball park to actual gross weight on water.
 If it is a little low, in effect that is like adding weight to the boat
 Gross weight coming in around the 500/600kg which based on info reading between the lines above is on the heavy side...
Also with shorter hulls it doesnt take much .. move the fish bin forward 500mm and engine height will change... real world stuff Wink

I had a a way to weigh a hull, on a single axle (or duel axle with 2 wheels off the ground from my old high school days 1/2 a century ago.. and lost it, now found.

Here it is..adapted to a boat on a trailer

 Did you know you can weight the boat (only the boat)  on the trailer with bathroom scales?

 keep the engine tilt as low was possible, but high enough to just clear the ground..

 measure all weights in lbs

 measure All distances in inches

1/Put the sales under the hitch, a length timber long enough to JUST lift the hitch and take the weight on the scales...  with trailer level or slightly low at the front.

record the weight  call it   w1

2/ slide the boat back on the trailer about 12" to 20"

 measure the distance accurately and record it  d1.. the accuracy of this measurement is very critical to the end result

 d1

3/ now with hitch same height record the weight as before You may not be able to move the boat a full 20" as the balance on the trailer may put the hitch up in the air....if so just move back till just have enough weight to measure at the hitch....OR put a known weight on the bow deck.. say a 40L water container full right at the start , before taking 1st weight (W1)

OR simply move a lot of stowed gear equipment well forward.

Measure this weight    w2

4/ now measure the distance from the center  where the bit of wood its on the scales to the center of the axle.

d2

 Boat weight = d2(w1-w2)/d1

If put an extra weight on the bow of the boat, now subtract that weight.

 Therefore if the constants like trailer weight... which we dont know we dont need that information because when the formula is compressed down that constant gets canceled out


Back to Top
Post Options Post Options   Likes (0) Likes(0)   Quote MacSkipper Quote  Post ReplyReply Direct Link To This Post Posted: 08 Oct 2019 at 4:42pm
MacSkipper View Drop Down
Titanium
Titanium
Avatar

Joined: 04 Jul 2014
Location: Manukau Harbour
Status: Offline
Points: 3727
Originally posted by Steps Steps wrote:

It is a Ratio 1.83 gearbox ratio right?
40hp 2 or 4 stroke?  2S
4.4m hull
WoT range 5000-5700

3500  27km/hr   (16.8 mph)
4000 33km/hr     (20.5mph)
4500 38km/hr     (23.6 )
5000 45km/hr     (28 )
5200 47km/hr WOT  (29.2 mph)

Prop pitch and diameter ? needed
Old alloy prop 11 1/4 x 13 new prop stainless 11 3/8 X 12 pitch

Sry need to keep data all together otherwise have to spend ages going thru back posts / pages digging info out
ratio gearbox 1.85 noted comments about weight in boat - by moving up to front of boat will effectively raise motor.
Good fishing trip nothing breaks, great trip catch fish.
Back to Top
Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 08 Oct 2019 at 6:37pm
Steps View Drop Down
Titanium
Titanium


Joined: 14 Oct 2013
Location: Sth Auckland
Status: Offline
Points: 8593
OK lets see what we get... with ratio 1.85
 pitch 12"
diam 11 3/8.

40hp 2 or 4 stroke?  2S
4.4m hull
WoT range 5000-5700

5200 WoT pretty well spot on for normal (??) loaded boat

3500  27km/hr   (16.8 mph)  22% 
4000 33km/hr     (20.5mph)    16.6% high for this weight boat.. 12/13 would be about ideal.
4500 38km/hr     (23.6 )         14.6% high
5000 45km/hr     (28 )           8.8  high
5200 47km/hr WOT  (29.2 mph)  8.6% still high 3.5 to 5% more ideal.

Good consistant data there..
You would now be in the fine tuning area.. that is for a general use boat all thats needed.. thu if a suitable pro came up cheap..$25/50 worth grabing ..even just for interest sake.. or a good spare.

So grip is a little loose..  extra cupping would not do what wanted. around another 1/4" diameter would work well.
 BUT
 That will also drop your 5200 WoT lower, estimate around 750 to 100 rpms... still in the manufactures spec, but in my books getting bit close to their limits of loading powerhead right thru the rpm range.
 As I have said we get the slip right (diameter) them work the pitch.
 So looking at around a   11 3/4" diameter X 11.5 " pitch with similar cupping as the current prop

I dont know what is available in sizing.

So lets look at what such a prop would do.
                       current                  predicted
4000   (20.5mph)   16.6%      4000 21mph 11% slip
5200   (29.2 mph)             approx 5200   29- 29.5   3.6-4.5%

Bottom line fine tuning would achieve next to nothing.. forget looking for a fine tune prop, the amount of fuel performance would be so insignificant wouldn't be worth the grease or time to change the prop over.

 I have posted this up.. as always do, doing calculations as I go...hence why above initially suggest,  maybe keep an eye open...
 It also illustrates well that target for a general use boat only needs to be a good ball park...fine tuning beyond that becomes pointless.

It is also very nice and preferred to confirm rather than correct a propping..and this is one of the best done so far.

As to moving gear around.. it does have its pros and cons.
moving stuff foward drops the bow but also increases surface area , drag (in effect makes the boat heavier.
If well powered (reserve power) that extra correction in height of the prop will level the boat and the bow wave will still remain just behind the middle of the boat at a good cruise speed.
 If not well powered

If experimenting with moving stuff around to get engine height.. including ppl.. keep that bow wave behind the middle of the hull.
 If engine doesnt lift then (in smaller boats) lift it
Back to Top
Post Options Post Options   Likes (0) Likes(0)   Quote MacSkipper Quote  Post ReplyReply Direct Link To This Post Posted: 09 Oct 2019 at 6:29pm
MacSkipper View Drop Down
Titanium
Titanium
Avatar

Joined: 04 Jul 2014
Location: Manukau Harbour
Status: Offline
Points: 3727
Originally posted by Steps Steps wrote:

OK lets see what we get... with ratio 1.85
 pitch 12"
diam 11 3/8.

40hp 2 or 4 stroke?  2S
4.4m hull
WoT range 5000-5700

5200 WoT pretty well spot on for normal (??) loaded boat

3500  27km/hr   (16.8 mph)  22% 
4000 33km/hr     (20.5mph)    16.6% high for this weight boat.. 12/13 would be about ideal.
4500 38km/hr     (23.6 )         14.6% high
5000 45km/hr     (28 )           8.8  high
5200 47km/hr WOT  (29.2 mph)  8.6% still high 3.5 to 5% more ideal.

Good consistant data there..
You would now be in the fine tuning area.. that is for a general use boat all thats needed.. thu if a suitable pro came up cheap..$25/50 worth grabing ..even just for interest sake.. or a good spare.

So grip is a little loose..  extra cupping would not do what wanted. around another 1/4" diameter would work well.
 BUT
 That will also drop your 5200 WoT lower, estimate around 750 to 100 rpms... still in the manufactures spec, but in my books getting bit close to their limits of loading powerhead right thru the rpm range.
 As I have said we get the slip right (diameter) them work the pitch.
 So looking at around a   11 3/4" diameter X 11.5 " pitch with similar cupping as the current prop

I dont know what is available in sizing.

So lets look at what such a prop would do.
                       current                  predicted
4000   (20.5mph)   16.6%      4000 21mph 11% slip
5200   (29.2 mph)             approx 5200   29- 29.5   3.6-4.5%

Bottom line fine tuning would achieve next to nothing.. forget looking for a fine tune prop, the amount of fuel performance would be so insignificant wouldn't be worth the grease or time to change the prop over.

 I have posted this up.. as always do, doing calculations as I go...hence why above initially suggest,  maybe keep an eye open...
 It also illustrates well that target for a general use boat only needs to be a good ball park...fine tuning beyond that becomes pointless.

It is also very nice and preferred to confirm rather than correct a propping..and this is one of the best done so far.

As to moving gear around.. it does have its pros and cons.
moving stuff foward drops the bow but also increases surface area , drag (in effect makes the boat heavier.
If well powered (reserve power) that extra correction in height of the prop will level the boat and the bow wave will still remain just behind the middle of the boat at a good cruise speed.
 If not well powered

If experimenting with moving stuff around to get engine height.. including ppl.. keep that bow wave behind the middle of the hull.
 If engine doesnt lift then (in smaller boats) lift it
Thanks Steps - I posted out of interest but was not intending to change anymore as very happy with mid range performance now which is what I look for as flat out top speed is here nor there...
Wondering about raising motor if a tad low but I noticed that when trimming for max speed 5000 rpm and above even a slight turn it starts to cavitate readily - if I bring motor in on trim it stops so I suspect I cannot improve much now anyway?
End of the day the hull design is what it is.
Good fishing trip nothing breaks, great trip catch fish.
Back to Top
Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 10 Oct 2019 at 8:48am
Steps View Drop Down
Titanium
Titanium


Joined: 14 Oct 2013
Location: Sth Auckland
Status: Offline
Points: 8593
I posted out of interest....
 Always good to know that your gut is confirmed right

Wondering about raising motor if a tad low but I noticed that when trimming for max speed 5000 rpm and above even a slight turn it starts to cavitate readily - if I bring motor in on trim it stops so I suspect I cannot improve much now anyway?

 If a engine is right or close as to right height, at best trim for that speed on flat water...in straight line.. you are already sitting on the limits of porpoising and or ventilation.
 Hit a bit chop or a wake, or disturb this 'balance' and yep should get a little ventilation.
 At lower speeds (rpms) not quite as sensitive.
Getting data is on flat water cause cant get best trim on disturbed water  (or going in 'circles')

In most cases when get a engine to ideal height (rem holes are 1" increments so usually close) in practice ends up dropping slightly low for real world conditions not always being flat water

On that basis I would then say you are already at good height.
 If anything mess with where stow a bit of gear, may even vary as to amount chop on the day in a smaller hull....
Being smaller rather than "design"
Back to Top
Page  <1 234
Forum Jump
Forum Permissions View Drop Down


This page was generated in 0.164 seconds.