Logo
FULL SITE MENU

potential 8.1 HO re-power advise

B

bobct

Advanced Contributor
My now 30 year old 454's have given me ten great years of service but the boat has always been underpowered (Trojan International, 33', 17k pounds fully loaded). I am looking a pair of 8.1 HO's as a bump up and a compromise between a full diesel re-power which I have taken off the table.

Right now, I'm cruising at about 16-17k knots and by all accounts a 20-21k cruise should be reasonable with the big jump in torque. Has anyone here done same on a boat of similar size and have feedback? I know I'll probably burn less fuel but keeping my expectations here really low. 10% less would be a homerun which should be reasonable.

- Is the footprint of the 8.1's very close to the 454's? I have the taller flame arrestor and still have a few additional inches of clearance above that.

- I have 1.25" shafts now and read that those should be ok if one is aquamet 22. I replaced one a few years ago and it is aquamet , the other is original but just dye tested last year.

- How do I determine the required transmission setup? The ones I'm looking at have ZF Hurth 630 A1 2.0 which I'm told are down angle units and believe that's what I need for my hull. On my model Trojan, the engines are set back and the shafts are pretty short and at a steep angle.
I assume the ratio is 2:1 but will verify. My current tran is 1.5:1.

thanks,
Bob
 
Biggest question I have is where are you gonna get them ??

The best answer on the gear probably comes from a marine architect......a good prop shop can share lots of experience as can a yard that specializes in repowers. More reduction will let the engine work easier.....

you can get the install drawing out of the Crusader installation manual, for the 8.1's.....I think I have some install drawings for the inline gear behind a 7.4 but won't have access for a few more hours...will email what I have later...
 
I have a Bertram Built Trojan 10 meter international with new Gen 6 FWC crusaders I will sell you the whole boat for 10K With a Kohler 5E Genset. I own too many boats.
 
makomark said:
Biggest question I have is where are you gonna get them ??

The best answer on the gear probably comes from a marine architect......a good prop shop can share lots of experience as can a yard that specializes in repowers. More reduction will let the engine work easier.....

you can get the install drawing out of the Crusader installation manual, for the 8.1's.....I think I have some install drawings for the inline gear behind a 7.4 but won't have access for a few more hours...will email what I have later...
Click to expand...

Mark,

Thanks, I called a prop shop who I've used before and they are going to send me something to figure out the props/transmission gearing.
To answer your first question, I have a lead a pair of used ones. Just doing some preliminary investigating and then might go see them this week.
Any dimensional drawings would help compare old vs. new. I "think" I have plenty of room but want to be sure.

Bob
 
Docksidemarineservices said:
I have a Bertram Built Trojan 10 meter international with new Gen 6 FWC crusaders I will sell you the whole boat for 10K With a Kohler 5E Genset. I own too many boats.
Click to expand...


Chris, that would be great option but I've put way to much time in customizing the one I have. Feel free to send me some pics though, I might know a guy who would be interested.

Bob

rdunne14 AT Comcast DOT net
 
sent you four drawings...one that should be close enough for your baseline and then the others are the 496 with various gears...
 
Back
Top