Powerplant swap Bertram 20

[arfaname]

Re: Powerplant swap Bertram 20

a quick update gents.

I have investigated thetacho and yes its wrong.. Nice pickup Mello. At 1000rpm the shop tach reads 750rpm. At 1600rpm the shop tach reads 1200rpm. i am making an assumption that at 6000rpm that its actually doing about 4400rpm working on 25%. I am also assuming no coincidence that an 8cyl with 25% less cylinders is a 6 cylinder.. ?>??????

 

[Bondo]

Re: Powerplant swap Bertram 20

I am also assuming no coincidence that an 8cyl with 25% less cylinders is a 6 cylinder.. ?>??????

Ayuh,... Assuming it's a coil driven Tach,... That's Right...

Does the Tach have a selector switch on the back of the gauge,..??
If so,... Switch it...

 

[arfaname]

Re: Powerplant swap Bertram 20

Nah unfortunatly not selectable Capt. I will source a replacement during the week. It is a coil driven Tach.

One thing I am pleased about is that it appears the prop and ratio may be close to correct.

 

[captmello]

Re: Powerplant swap Bertram 20

One thing I am pleased about is that it appears the prop and ratio may be close to correct.

Yes, according to your shop tach, you're right on. A new tach should be an easy fix.

Happy boating!!!

 

[arfaname]

Re: Powerplant swap Bertram 20

Oh how time flies..

Sorry about the delay fellas but I've been out fishin

Well it has all come together and i have put some 200 + km on the old girl. It is going really well. I havent yet overcome the revs issue but simply dont over rev it for now. The local prop shops around here arent all that helpful and odnt stock the prop I require to "try b4 i buy" .

Well anyway below are some more pics.

Holes for through hull

Exhaust tips fitted.

Motor in the hole for good.

New alternator bracket to highmount it. No room below.

 

[arfaname]

Re: Powerplant swap Bertram 20

And out there getting amoungst it..

Capt,

The engine mounts have a small section of rubber between them for vibration. They are bolted right through the stringer with a metal plate behind to spread the load.

 

[captmello]

Re: Powerplant swap Bertram 20

Great to see the update!!

Man, that engine couldn't be any tighter in your boat.

Hope the starter doesn't go out soon, Looks like an engine pull for that job.

Like stated early in your thread, great lookin' boat. Definitely worthy of the repower.

Our spring is apon us up here!!

Good luck with your boating and fishing.

 

[triman]

Re: Powerplant swap Bertram 20

She scrubbed up a treat, nice looking job. What did you end up with as an engine cover, and do you find with the cover in place you have good fish-working space?

 

[Dunaruna]

Re: Powerplant swap Bertram 20

Sean, a couple of weeks ago I saw that beast parked in front of Yarra Valley toyota, do you work in Croydon? (I suspect the answer is yes, the tow vehicle had signwriting for an electrical supplier on Lacey street).

 

[arfaname]

Re: Powerplant swap Bertram 20

Well Capt,, yup, shes pretty tight mate... I guess the beauty is that I can pull the donk in under an hour if I ever do need to change a starter motor. The good thing about how well it looks is that it now goes just as well as it looks.

Triman,

As a temporary measure I "pumped the sides" of the existing cover. By cutting out the side panels where the risers sit I was able to screw some timber in between the two parts creating an extra 80mm each side. My long term plean is/was to glass over the lot, fill, rub and paint the whole lot. However , on ebay this week I have stumbled across a brand new cover that will fit with a little gentle persuasion. I should have that by this wednesday.

Aldo,

Yup, thats it bud. I run CNW in Croydon there. You will see the old girl there often. If you see it there mate drop in for a look see if you like. If I can help you with any electrical bits, just ask. Im off to Portland Tuna fishing this weekend so it will be out front Friday.


As for the revs issue, I think I stated earlier that I woudl change the tacho and have done so. I am convinced it is now correct but still revving 5800-6000rpm at 75km/h. I have checked the ratio and im running the correct 1.61 and the prop is stamped 14x21L. I measured the prop on the weekend and decided that it measured as 24 inch pitch. I used this site as my method http://www.propellerpages.com/?c=articles&f=2006-03-27_manual_pitch_measurement .

Is it possible that because its running a fair amount of HP that with the standard ratio and the standard prop are simply not suitable for that boat? If so, which way do I go now? How far can I go in pitch for the VP280 leg? Can I get a lower ratio gear set for the bottom box?

What do you blokes think?

I am also finding it is porpoising at 70-75km/h. I have considered both Permatrim and trim tabs but unsure which way to go. I need to get the nose down.

Aldo, you may be able to answer (cast your mind way back)(I bought Aldos old boat but is now gone) When you put the permatrim on Dunarunna do it create a big improvement and if so in which way? I nearly scored the old permatrim back last week but he renegged.. Doh.. lol


Thanks for your interest fellas.


Sean

 

[achris]

Re: Powerplant swap Bertram 20

...I am also finding it is porpoising at 70-75km/h. I have considered both Permatrim and trim tabs but unsure which way to go. I need to get the nose down....

They do that... I've had mine at 80km/h and it's a handful. I don't think the hull was design for more than about 35knots (65km/hr). I'm also considering tabs. It should also make the boat better in the 14-20 knot range too... With some decent weather I usually find around 17 knots is a good speed.

A few years back I wrote a program to check all those funny figures (Speed, ratio, revs, ect) and by my program it looks like your tacho is still reading way high.... See screen grab below....

Chris...

 

[Dunaruna]

Re: Powerplant swap Bertram 20

The reefrunna was a slug out of the hole because i had it propped for trolling. The permatrim fixed the holes hot issue. One of the downsides was it caused a lot of wandering at slow speeds although i suspect there was a slight hook in the keel. She never porpoised, with or without the permatrim.

Bottom line is that it had good and bad points, it's performance characteristics would differ from boat to boat.

 

[captmello]

Re: Powerplant swap Bertram 20

Ya, your tach is not right. Like Achris's numbers show, 50% slip??? Are you sure the new tach is set for a V8 engine?

I've got the same power train as you in a lighter weight boat. I run a 21p prop and max out at 4400RPM. With more pitch I would loose RPM. I would think you would want a 21p or even 19p. But first you've got to get the tach reading right. You need the WOT RPM's between 4000-4400.

Have you tried adjusting the Stainless rod on the outdrive. There are three holes you can use to slightly adjust the trim of the outdrive. You may need to move the rod in towards the transom one hole to lower the bow a bit and cut down on the porpoising.