Lord Farringdon, Richard F, Clasg, Oldskool. Have a look at this.

[melida]

Terry, Richard, Clasg and Bill.

As you are KAD300 owners and Bill as a Volvo Specialist could you evaluate the water spray over my caviation plate ?

Do you guys have the same spray or I'm doing something wrong ?

Is it an indicator as overtrimmed ? Though keeping the drive at that position than lowering didn't cause any speed loss.

I have no KAD300 DP_G owners in this off season around me to discuss it.

This video was shot yesterday while on plane at 3200rpm 20 knots, drive at 0 degree, trim tabs fully retracted heading towards cross wind head/beam.

Ride was comfortable and no difference since day one I purchased the boat.

[video=youtube_share;y1E9RQ0Qbbs]http://youtu.be/y1E9RQ0Qbbs[/video]

 

[andy k]

Looks a little dangerous leaning over your swim platform when you are on plane. :wow:

But from what I can tell it looks normal.

 

[Lord Farringdon]

Hi Sayat

I think your swim platform must sit much higher than mine because I doubt I could get a photo of my drive like that. So far as the spray from the cavitation plate is concerned I would think this is normal with the drive that far out of the water.

I find your wake pattern to quite a lot different to mine. I guess our hulls are a little different but not that different. Still, you seem to be generating quite a 'rooster tail' and there is a lot of frothy water churned by the prop which seems to be in a long trail in the centre of the wake for some distance. Compare this to my wake (on a smoother sea granted and with a little zoom I think) and there is an absence of this centre disturbance in the water except immediately after the prop. This kind of suggests I have my drive trimmed a lot further down than yours and in practice the one time I ran with the drive trimmed up I had some major cavitation on the props which took off the newly applied prop speed! I am also at 20 kts and 3300-3400 rpm. It looks slower than your wake but I suspect that is the difference in the sea condition and the zoom factor having some effect. My physics education tells me it takes energy to disturb all that water which is lost to pushing the boat through the water. And if all that froth is being created maybe there is some cavitation there too?

So, maybe you could try trimming the drive further down and see what that does to the wake pattern. Does it reduce that centre froth? Does it reduce the cavitation plate spray? I wonder if there are any "wake experts" out there?


Take care around that swim platform while underway Sayat. I wouldn't like to hear you had a sudden immersion at speed episode!!


Terry

 

[melida]

Looks a little dangerous leaning over your swim platform when you are on plane. :wow:

But from what I can tell it looks normal.

You're right but I was holding the stern locker grab rail with my left hand and camera on the right and sitting on the knees.

Is it also same spray with the Bravo drive as you have ?

 

[melida]

Hi Sayat

I think your swim platform must sit much higher than mine because I doubt I could get a photo of my drive like that. So far as the spray from the cavitation plate is concerned I would think this is normal with the drive that far out of the water.

I find your wake pattern to quite a lot different to mine. I guess our hulls are a little different but not that different. Still, you seem to be generating quite a 'rooster tail' and there is a lot of frothy water churned by the prop which seems to be in a long trail in the centre of the wake for some distance. Compare this to my wake (on a smoother sea granted and with a little zoom I think) and there is an absence of this centre disturbance in the water except immediately after the prop. This kind of suggests I have my drive trimmed a lot further down than yours and in practice the one time I ran with the drive trimmed up I had some major cavitation on the props which took off the newly applied prop speed! I am also at 20 kts and 3300-3400 rpm. It looks slower than your wake but I suspect that is the difference in the sea condition and the zoom factor having some effect. My physics education tells me it takes energy to disturb all that water which is lost to pushing the boat through the water. And if all that froth is being created maybe there is some cavitation there too?

So, maybe you could try trimming the drive further down and see what that does to the wake pattern. Does it reduce that centre froth? Does it reduce the cavitation plate spray? I wonder if there are any "wake experts" out there?


Take care around that swim platform while underway Sayat. I wouldn't like to hear you had a sudden immersion at speed episode!!


Terry

Terry,
Hi again.
Since my boat has single engine even with full fuel, full water + hwh and 4-6 people , while on plane it’s at same height as light weight as seen in the video.

Keeping the drive at 0 degree and retracting the tabs fully lifts the boat too much sensible and speed increases to.

Below pics are at stationary.

What I know about the wake and rooster tail is should be away from stern and flat while on plane. Near to stern and high/curling means you are off plane or drive is maximum down. So mine seems normal.
It’s interesting that you mentioned in an other thread of mine you should keep your drive in -1 at wot -5 at cruise. This leads the wake and rooster tail near to stern and high/curling . Also strange that when you run faster, trimming the drive + degrees decreases your speed. Something seems wrong with your drive settings. Either the trim gauge, trim sender or drive calibration. You may have check that in the haul out and set the drive to -9 at fully down.

Trim tabs down, drive at 0 degree

A few shot of my wake and rooster tail while on plane/optimum cruise in different time

Running at 3500rpm, 25knot, +5 drive trim, trim tabs fully retracted.

Thanks for the good wishes my friend.
Safety first.

 

[Lord Farringdon]

Hi Sayat,

You are right. There seems to be a definite difference in the trim condition of our two boats. You trim up and I trim down. However, I dont take too much notice of the trim gauge so far as optimum speed is concerned and prefer to use the GPS speed as a good indicator of if the drive and tabs are trimmed properly. I aslo find the trim indicator reads differnetly depneding on which Volvo tech last took the drive off for servicing. They seem to get the trim sensor gear rack out by one tooth in one direction or the other! Having said that, the last tech got it right in accordance with the stern drive workshop manual with the lowest position being -7.

If your max trim down condition is -9, then I wonder if your gear rack is out by one tooth?

You trim shallower and I trim deeper . I wonder if this is to do with slightly different hull shapes, weight, wind drag or centre of gravity differences?

I have attached a video of my wake which is the same as yours except yours seems to have stronger centreline of white which is in keeping with your drive being trimmed up rather than down.



Terry

 

[melida]

Hi Sayat,

You are right. There seems to be a definite difference in the trim condition of our two boats. You trim up and I trim down. However, I dont take too much notice of the trim gauge so far as optimum speed is concerned and prefer to use the GPS speed as a good indicator of if the drive and tabs are trimmed properly. I aslo find the trim indicator reads differnetly depneding on which Volvo tech last took the drive off for servicing. They seem to get the trim sensor gear rack out by one tooth in one direction or the other! Having said that, the last tech got it right in accordance with the stern drive workshop manual with the lowest position being -7.

If your max trim down condition is -9, then I wonder if your gear rack is out by one tooth?

You trim shallower and I trim deeper . I wonder if this is to do with slightly different hull shapes, weight, wind drag or centre of gravity differences?

I have attached a video of my wake which is the same as yours except yours seems to have stronger centreline of white which is in keeping with your drive being trimmed up rather than down.



Terry

Terry,

My boat specified 3856 kg from factory with single 496MAG B3 setup, 21degree dead rise and 8,69m water line length whereas 9,47 LOA. KAD300 has the same weight with 496MAG. Over this weight add A/C, inverter, radar, gps, autopilot, fish finder, bow thruster, hydronic heating camper canvas, windlass, anchor, 50m chain and a few light weight options, toolbox, spare parts and fluids, maintenance items makes the boat app. 4000-4050kgs. Add to these 100 gallon diesel= 387,54Liters x 0,832 kg/L=315kg, fuel tank 106 liter=106kg, hot water heater 22,7liter=22,7kg equals to 4494kg.
Oh forgot to add me, even boat has autopilot but someone has to touch that button so add 103kg with clothes made the boat 4600kg without wife, daughter, dingy and motor and others/guests.

Since the engine is diesel and consumes 3-4 times less than the gas version, decreasing the fixed weight of the boat takes long time.

Quick look back to your boat.

2005 270AJ specified 3323kg with 350MAG B3 setup, so we should add app 100kg for KAD300, 21degree dead rise and 8,36m water line length whereas 9,14 LOA. Also you have 100 gallon diesel tank 28gallon water and 6 gallon hot water heater makes 3323+100+315+106+22, 7=3866, 7kg without you.
Don’t know which options and upgrades you have so assuming you are 100kg and another 100kg for extras without your wife and any other people on board, made the boat 4067 kg.

So even we have very similar boat as hull shape and small length difference however mine has a beam of 2,87m and yours is 2,59m.

So you have the both advantage in terms of length, width and over 500kg of weight.

SO why my bigger and heavier boat performs better than yours about trim settings and speed?

Let’s compare our performances.

When I bought my boat it had factory C4 props and 35cmx35cm stock trim tabs.

With that setup full fuel, full water and hwh and only me onboard, campers on, dinghy and motor on the swim platform she planned at 3000rpm at 18.5 knots, trim tabs fully retracted and drive trim at 0 degree.

Over above weight wife came onboard and we couldn’t got on plane. When the fuel decreased below ¾ then we could. Over 3 people onboard again struggled, but at ½ fuel 6-7 people didn’t mattered.

I wasn’t happy with this and bought C3 props. But could plane at 3500rpm again at 18.5 knots whereas C4 props give 25 knots at 3500rpm.

Again I wasn’t happy with this and put the C4 set and enlarged the trim tabs to 40cmx50cm. She did what should be. After 2 years of enlarging them I’m happy with that and with “clean props” full fuel and water, 6 people onboard I can plane with no problem.

BUT you have C2 props (3860877,3860602LH,3860603RH part number), I wonder if they aren’t C3 (3860878,3860604LH,3860605RH part number) ?

I don’t think so my boat could plane with C2s while with C3s she needs to reach 3500rpm.

But your initial weight is 500kg less than mine so with a two size smaller prop set you could plane.

As you know lowering the pitch of props makes easier to get out of the hole but decreases top end speed a couple knots. I did 28,7knots with C3s while I can easily do 31,5knots with C4s and the more boat have less weight she reaches to 35knots.

With my all prop sets and trim tabs I always cruised at 0+1+2 degrees and +5 at 3500rpm and wot.

Trimming the drive down needed to stay on plane at bad weather or low speeds.

So by keeping the drive all the way down or -1 you are forcing your boat to stay on plane with low speed, this also increases fuel consumption.

It seems that your boat needs more speed to stay on plane to keep the drive at 0 degree.

IMO you must put 1 size bigger prop set than what you have now.
If’d be you I’d give a try with a bigger prop set and/or enlarging the trim tabs.

On the other hand, every boat has its own characteristics, so playing with props and trim tabs may not solve this.

Lets look at the drive trim settings.

It’s good news that you’ve set it to -7, so there is some room for improvement. Is there positive change after setting to -7 or same as before ?

When I first bought mine set to -5 then my mech set it to -8. If he sets it to -9 the rack goes out of line. When I leave my boat trim the drive fully down as same as when I anchor, trim pump makes the zzzz noise at -7 then gauge shows -8.

But at underway before plane I trim the drive fully down to -8 as well as deploy the trim tabs, after exceeding hull speed gauge shows -9. Also after plane before hit or roll over a wave when I lower the drive again it goes to -9. This is what I do in last 3 years of ownership and the trim racks stays in it's place.

Also there is neither harm to the drive components nor to the propellers as well as no cavitations and burn.

After 400 hours in 6,5 years of salt water use.

As you see in the above pic there is no problem of props while you have cavitation and burn over yours and interestingly your propspeed have lost. Contrary I applied 2 spray bottles of international prep-o-drev primer and antifouling to my props at May 10, 2011 there were barnacles covered over them at the end of june and I couldn’t got on plane. This year I thought to not painting my hull and drive, only gonna haul out to change the drive oil and zincs and if needed bellows.

Some pics of mine to compare with your's, how much the trim piston travels at respective trim angle.

Drive at 0 degree.

Drive fully down or -7-8

Drive fully up at 40 degree.

Your video shows exactly you’re trimmed all the way down and wake close to stern whereas mine is far away from stern.

Do you have any other people with VP KAD300 or 44 or any VP diesel around you to discuss and compare your wake ?

I’m sure if you put 1 size larger props you’ll perform better both speed/consumption and upper drive trim.

Stay tuned.
Cheers my friend.

 

[Lord Farringdon]

Hi Sayat,

Hi Sayat,
Thanks for the in-depth analysis. I'm pretty sure you are right. I'm a little underpropped. Need C3's. I suspect the dealer in NZ put C2's on because the C6's were just way to big and he didn't have any C3 or C4's in stock. I would like to try a set of C3's first though so I will have to talk to my Vovlo guys and see if they can help me. Unfortunately, I doubt they hold expensive sets of props just sitting around waiting to be tried out! This has started me researching I have been searching on Boat Design forums for information. I'm a bit busy with other things at the moment Sayat and will get back to you on this subject in a little while, once I've figured a few things out. Once again, thanks for the excellent analysis.


Terry