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  1. #51

    Re: 46 Convertible refit begins

    Looks great, Mick.

    Presumably, rebuilds will cost roughly the same whether it's your 871s or 692s. So the 25 k au you mentioned is buying the added HP. IIRC, you mentioned before that you'd be inclined to just pull back the sticks, which I took to mean you tend to cruise or don't mind cruising at relatively low speed. One of the other fellas here mentioned the 92s have issues the 71s don't have, which is why I thought rebuilding the 871s seemed like a better approach, especially for a lower speed cruiser.

    Cheers,
    Q

  2. #52

    Re: 46 Convertible refit begins

    Quote Originally Posted by Mick c View Post
    Based on the info what everyone’s thoughts on the rational ? Regards Mick
    Just my opinion, but I think you are overpaying for the 6v92 detroits.
    FTFD... i drive a slow 1968 41c381

  3. #53

    Re: 46 Convertible refit begins

    Quote Originally Posted by q240z View Post
    Looks great, Mick.Presumably, rebuilds will cost roughly the same whether it's your 871s or 692s. So the 25 k au you mentioned is buying the added HP. IIRC, you mentioned before that you'd be inclined to just pull back the sticks, which I took to mean you tend to cruise or don't mind cruising at relatively low speed. One of the other fellas here mentioned the 92s have issues the 71s don't have, which is why I thought rebuilding the 871s seemed like a better approach, especially for a lower speed cruiser.Cheers,Q
    I hear what you guys are saying and yes it is a little contradictory to what I have mentioned in some of my last posts but unfortunately we are rev heads at heart and we always tend to go in that direction eventually. Our prop guy has done the calcs on the boat/gearbox’s and prop combo and suggests that we most likely what we wil achieve around 26-28 knots which I wouldn’t regard as outrageously powerful. Anyhow I do appreciate all the feedback we get good or bad. Mick

  4. #54

    Re: 46 Convertible refit begins

    Hi, I have a 1982 46C HP, 8V92Ti 650 hp. Allison MH transmission weight 20 tons. Max rpm 2300. At WOT with half fuel she will do 27knots. Although very smooth, I feel for the old girl. With FULL fuel ( 2400 liter ); if I generally cruise at 20 knots, Do a little trolling and Bring it up to full throttle for short times I can go about 200 miles. If I generally do 8 to 9 knots, a little fishing and bring it up to WOT a couple times for about 15 min, I can go well over 400 miles. I believe that the best reason for more HP is for when you need the boat to preform, not just to go Fast. The weather here tends to change without notice. It is nice to have good response when the seas become nasty. In your apparent situation, I would keep it simple, stay with the smaller 71's. If you really want the extra work, cost and HP, Change your budget and get modern 4 strokes. The higher HP Detroit's require a lot of TLC to stay clean. I recently rebuilt my starboard engine with the aid of a manual, very straight forward. Even if they look good, buy new exhaust manifolds and risers. Rebuild the injectors. I also bought new turbos and have rebuilt one of the old ones for a spare. the hardest part was the weight of the parts and that I am on a mooring. All the best, Have fun.

    Pete

  5. #55

    Re: 46 Convertible refit begins

    Quote Originally Posted by osprey View Post
    Hi, I have a 1982 46C HP, 8V92Ti 650 hp. Allison MH transmission weight 20 tons. Max rpm 2300. At WOT with half fuel she will do 27knots. Although very smooth, I feel for the old girl. With FULL fuel ( 2400 liter ); if I generally cruise at 20 knots, Do a little trolling and Bring it up to full throttle for short times I can go about 200 miles. If I generally do 8 to 9 knots, a little fishing and bring it up to WOT a couple times for about 15 min, I can go well over 400 miles. I believe that the best reason for more HP is for when you need the boat to preform, not just to go Fast. The weather here tends to change without notice. It is nice to have good response when the seas become nasty. In your apparent situation, I would keep it simple, stay with the smaller 71's. If you really want the extra work, cost and HP, Change your budget and get modern 4 strokes. The higher HP Detroit's require a lot of TLC to stay clean. I recently rebuilt my starboard engine with the aid of a manual, very straight forward. Even if they look good, buy new exhaust manifolds and risers. Rebuild the injectors. I also bought new turbos and have rebuilt one of the old ones for a spare. the hardest part was the weight of the parts and that I am on a mooring. All the best, Have fun.Pete
    Thanks Pete, sounds like my prop guy estimated correctly when he said the boat should do about 26-28 knots based on the performance of your boat. The big difference for me is that these particular 92 are electronic over the old 71s and yes I would love to fit a couple of Cummins into the boat but that will add at least 150 k au to the project. Maybe later. I would rather be cruising at 16 odd knots with the 92 than ringing the neck out of the 71 s ?. What props are you running with what shaft size.?

  6. #56

    Re: 46 Convertible refit begins

    Quote Originally Posted by Dazed338 View Post
    Nice, love the beam setup
    Thanks for that. Spent a lot of time planning the removal of the engines. The hired gantry was extremely adjustable and modular. It helped having the machinery skates under the gantry for sideways movement as well. Had about 0 clearance out the door but all in all went to plan. Mick

  7. #57

    Re: 46 Convertible refit begins

    Hi Mike, I have 2.5 inch shaft and am running 28 x 26 four bladed props. The original 3 blade props 28 x 27 where also pretty good, but only could get about 25knots. I changed them for my spare set because the 3 blade props needed to be tuned.

    Have fun,

    Pete

  8. #58

    Re: 46 Convertible refit begins

    A thought on Speed, My 46C feel good hull speed is about 8 to 9 knots at about 850 rpm. More rpm and I start pushing water. At which point I would push up to 2100 rpm, get her on the plan and will do a little more then 22 knots then slowly retard engines to settle into about 1850 rpm cruising at about 20knots. On a good day I can throttle back to a little over 1650 rpm and she will glide along at 17knots. any slower or if there's a bit of wave action, she will fall off the plane. 11 thru 16knots are not speeds I can use. Pete

  9. #59

    Re: 46 Convertible refit begins

    IT really sounds like every boat and every engine and prop combo has different outcomes. I guess we won’t know till we get it back in the water. Thanks M

  10. #60

    Re: 46 Convertible refit begins

    I think the reason that people are questioning your plan to go with 92 series DDs is that theya re very intolerant of overheating- the silicone seals at the end of the liners can leak if they are run too hot, and apparently if the cooling system isn't up to snuff they WILL run hot. And when they leak, it is easy to really damage the engine, and it all happens pretty fast.

    It seems to me (from half a world away, granted) that you should either keep our 8-71s, or look for modern 4-stroke engines, which would preferably be Cummins M11s. I think the 92 series will cost you a lot, and not get you that much additional performance...

    Of course, it's easy to give advice, and the free advice here, including mine, will be worth what you pay for it. Maybe the best way to proceed is to clean up the boat and do all the updates and keep thinking about what engines you want to put in. After all, you have a lot of prep work to do before anything goes back in, so maybe you don't have to make a decision right away.

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