Home Decor Underwater Prop Change

I've ever had a suspicion my prop was undersized for the boat in addition to the type of waterways nosotros create in addition to intend to usage it on. The engine never seemed to endure "working" which is non ideal for a diesel fuel in addition to is only really used at the lower rev range.

I did some interrogation into the real dark fine art of prop calculation, at start online amongst diverse spider web based calculators hence amongst virtually one-half a dozen Great Britain based prop manufacturers.  In all cases the maximum diameter I tin swing is a 21" hence this was a definite as likewise was the max RPM, HP, in addition to gear ratios in addition to the hull size in addition to weight.

All online in addition to all manufacturers calculations came upwardly amongst the same pitch inside an inch or 2,  with most pitching at the mid gain of 21.  So it was decided a 21 x 21 in addition to yet a 4 blade. Up from 21 x 16.



Old in addition to novel props side past times side

The initial invention was move a elevator out in addition to the dorsum the same twenty-four hr menstruation at a local crane day, but the to a greater extent than I looked at it in addition to them to a greater extent than advice I sought I decided it would endure worth at to the lowest degree trying to create it nether water. If this didn't move or something serious happened the crane was yet an option.

I'm fortunate that the weed hatch on the boat is quite large in addition to access expert in addition to Garth at the boat yard had the necessary prop puller on hand.


Weed hatch

The prop nut on a Vetus shaft is a flange nut hence at that topographic point would endure no work amongst either lining upwardly a nut in addition to split upwardly pivot hole or having to drill a novel one.  The only downwards side was ii 2mm thick SS flanges had to endure hack sawn off in addition to hack saw stimulate was limited.  This usage of the labor took a quite painful hr or so, but in i lawsuit done the nut was easily removed.

Prop nut showing the flats where the flanges lock

Old prop, nut removed

Then getting the prop puller on was a flake of a fiddle but virtually one-half an hr of adjustment had it create to start winding on the pressure.

Lots of lines attached hence every bit non to lose anything

After a flake to a greater extent than tightening that sweetness minute the taper broke.  The prop was off. :-)


This lot was removed in addition to the novel prop offered on the the shaft in addition to measurements taken to flora the telephone substitution wouldn't endure likewise proud for the novel prop.  I was undecided that the prop would sit down solely on the taper in addition to non the key.  In the terminate I decided it was belike fine but removing .5mm would create no price hence I did this gently in addition to ended up, in i lawsuit it was apartment in addition to foursquare again, at .7mm removed.


Then it was fourth dimension to gibe the novel prop.

All consummate amongst shaft anode refitted

In all it took closed to vi hours, in addition to of course of teaching the only usage dropped was the non ferrous prop nut which required the donning of  the moisture suit in addition to snorkel in addition to a curt dive to the river bed virtually 4' downwards to recall it.

All inwards all a expert days move in addition to a worthwhile experience. 

The purpose was to charge the engine a flake to a greater extent than at every bit the xvi was non making the engine move in addition to would easily accomplish max RPM of 2500 which is never needed or used. Also I wanted the fast cruise RPM to endure at the gain of the torque curve at 1500rpm.

RPM             Speed MPH

                   Previously 16".          Now 21".
  800            2.6                          4
1000            3.5                          4.8
1200            
4.5                          5.5
1500            4.8                          6.5    Turbo forthwith heard working
1800            6.0                          7.8    And speed building


I suspect given all the correct weather 8.5mph would be achievable.

The weather were air current on against 2 mph (ish) flow.

Observations hence far are noticeably less rudder judder throughout the range, to a greater extent than rudder authority, less rudder input to move along on line, turbo heard working, acceleration much ameliorate (not actually required) stopping massively improved prop walk slightly to a greater extent than pronounced, engine ran 5°c hotter on prolonged 1800+ exam but this returned to normal 85°c real rapidly at 1500 in addition to maximum rpm forthwith 2200 hence slightly over propped every bit expected. No dark smoke at whatsoever betoken on the test.

In decision I think this has been worthwhile. I tin forthwith cruise real nicely at M in addition to fast cruise at 1500 in addition to gallop at 1800.

These are only preliminary tests on deep H2O hence similar all things boat at that topographic point are infinite variables.

The predicted all round performance/economy improvement was 20% which I think is belike virtually right.  Someone else tin create the calculations for me if they like.

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