GB46 repower outcome – thank you to this forum

[BrisHamish]

I posted some questions on this forum about repowering my 2006 Grand Banks 46eu in Brisbane, Australia and received helpful responses, plus I read and learned heaps from the articles available here. So, on the basis that some might be interested in the final outcome, attached are some photos of the repower process and the final product, for those interested.

Previous engines were CAT C7s at 455hp, the PO had aftercooler failures which let salt water get into the engine cores in about 2008. By 2020 the inlet valves and No 1 cylinder on each were badly rusted and there was a loud ‘knock’ from No 1 cylinder where (I will describe this poorly, pls excuse my lack of proper technical description) the borescope inspection revealed the cross hatching on the No 1 cylinder walls was sort of eaten away and rusted.

I ended up choosing new QSC8.3 at 550hp, and redid all the electrics/batteries and the fuel lines. We have had several goes at the props (hauling the boat each time) to get the pitch right such that we are below the Cummins fuel use curve for this engine model. (Props had to be cut down, and also pitch reduced from 23’’ then to 21’’ and then to 20.5’’).

End result is much smoother and quieter engines, no smoke at all, and actually lower fuel use when running at the same speed compared with the previous CATs.

Huge thank you to everyone on this forum and all the super useful information made available here free of charge to those who are interested. It’s a great site.

Thanks,

Hamish.

3 users thanked author for this post.

Rob Schepis, Tony Athens, Scotth

Topic

[BrisHamish]

Hi all,

Good question re what power we use. Typically we cruise at 11 to 12 knots, the hull is SD design, and I find that at that speed the boat ‘sits up’ a little better (compared to say 8 knots) and the Naiad stabilisers are just that bit more effective/quick to catch the roll.

We usually take the boat north to the Great Barrier Reef each year, and there is a bar on the way (Google ‘Wide Bay Bar Queensland’) where you use every single bit of power you have got…But that’s only twice a year, and most other times it 2300rpm or so (out of 3000 available for these engines).

At any speed, even when she sort of gets ‘up on the plane’ at say 16 knots and 2600 rpm and a forgiving tide, my boat is always pushing a wake in front and she is heavy. Hence my desire during the repower process for bigger displacement engines – the old C7s were 7.1litre – and the choice of QSC rather then QSB, as there is always (what I would describe as) a ‘torque demand’ at any speed on this boat. I may be wrong about that, but it was my thinking.

Cummins was the third most expensive option out of all the brands I investigated (CAT, Nanni, Deere, Yanmar, Volvo), but far and away the best to deal with. Other posts on this site reference Rudi Wehrend and the Cummins people in Brisbane Australia (Justin in sales and Lindsay in engineering).

Finally, I did pull apart and grease the aftercoolers prior to first use as per SBMAR protocol. It wont show in the photos, because I resprayed the bolts afterwards! Interestingly, similar manufacture dates on each of the engine, but one had some grease (not enough) on the aftercoolers when we pulled them apart, the other had absolutely zero! So worth doing, definitely.

Thank you again.

[Tony Athens]

Looks like to “went for it” and did not cut any corners……………………………….All looks really good..

Curious, do you really use all the HP ? Seems to me a boat like this is most enjoyable during the journey at 7-11 Kts, i.e. the “wine & cheese” cruise mode getting 2 MPG or better..

[Author]

Replies