28 topaz...diesel or gas???

[controlled chaos]

alright guys, here is the deal.

My dad just passed on his old work boat to me. It has been sitting for 12 years so it needs plenty of work but I grew up on the boat so when he said he wanted to get rid of it then I quickly claimed it as my own. It is a 1978 28 foot topaz makaira that was transformed into a towboat with twin 454s and 1.91:1 borg warners. it swung 18x24 4 blades and he got about 4000 hours out of those engines and averaged about 1 nmpg at cruise. The question of the day is.... when it is time to repower should I have the big blocks rebuilt or should I go to a diesel? This is not a boat that will be sold after its completed so I am not concerned with resale value at all. I just want a few opinions on the boat and projected power. If I go with diesels will they really be that much better on fuel? I guess if the diesels gave an extra 1.5 nmpg then it would be worth it in the long run but I am not sure this boat is capable of getting fuel economy better than 2 nmpg at most. Another thing is hp ratings. I dont want to throw in underpowered diesels like most of the 28 topaz boats have. I want to be able to cruise at a decent speed and have extra power if it is needed. The boat cruised at 30kts with 454s in it and topped out at 45+kts. I think the cummins 5.9s can get me in that area but I am not totally sure. So please feel free to comment and recommend different setups because I am all ears.

thanks a lot fellas

DK

[crmarlinfisher]

diesel is better

[Ultralite]

A friend has the Topaz 28 Express and it was powered with twin Volvo 40 series diesels (165 hp). He finally blew one engine and is repowering with rebuilt 41B series diesels. The boat would cruise 18 to 20 knots and got 1.5 nmpg with the 40s. I seriously doubt that you would ever see over 2.0 nmpg with diesels in that boat.

[controlled chaos]

thanks guys, ultralight, thats kinda what I was thinking as far as fuel mileage goes. I really like diesels and in my truck I would have nothing other than a big diesel but as far as the boat goes, 2 diesels are gonna set me back at least 30K and the returns are not gonna be that great. I guess I should just go with the gassers on this one so I can have more dough left over to buy gear and other stuff that I "need". haha.

thanks

DK

[Logan9581]

find a steyr dealer and talk with them.
http://www.steyr-motors.com

We have a single 256 in our 27 Oceanmaster and get a 30 mph cruise.

[seapower]

If you're serious 30k is just a starting point. There's alot more involved than just "dropping" a diesel in. Frank,SeaPower

[jawz12]

If you're serious 30k is just a starting point. There's alot more involved than just "dropping" a diesel in. Frank,SeaPower

excellent point !!!
there's alot more...first,you need and exhaust system that will flow for diesels,then,you're gonna need fittings in the tanks for return lines,additional filters-racors,shafts,wheels,batteries-etc...it keeps going...there's stuff required i didn't even mention..such as,in some cases,the need to supply more air into the engine room...

i repowered a similar rig,it had old 40 series volvos in it,i dropped in a new set of 41 series volvos-the old 40's were the 135 hp version,the 41's are 210hp...that rig ran real well,2.5nmpg if i recall correctly,owner was very happy witht he new power...

[Day Tripper]

SF
I have a 1977 28' topaz with twin 210HP Cummins. The boat runs great on diesel. A few weeks ago I ran 62 miles out trolled 7 hours and ran back and burned 107 gallons. The boat cruises at 22-24 knots at 2200 rpm pull it back a little and you'll save more fuel. You can get a pair of 210's for around
25K I have 220A ZF gears 1.53 ratio
let me know if you have any other questions
Tim

[Avenger]

First, let me say that I am a diesel guy through and through. I make my living repairing them, so you know I'm biased. With that being said I have to tell you that unless you need the extra range you'll be throwing your money away if you put diesels in.

The engines will cost more to buy, more to install and more to maintain. A LOT more. You will never even approach recovering the costs with fuel economy. So unless you run a thousand hours a year (literally) or need to maximize range you'll do better all around with gas. If the boat was 35 ft or bigger it might be worth considering but for a 28 you've already got the right power.

[Mackey]

First, let me say that I am a diesel guy through and through. I make my living repairing them, so you know I'm biased. With that being said I have to tell you that unless you need the extra range you'll be throwing your money away if you put diesels in.

The engines will cost more to buy, more to install and more to maintain. A LOT more. You will never even approach recovering the costs with fuel economy. So unless you run a thousand hours a year (literally) or need to maximize range you'll do better all around with gas. If the boat was 35 ft or bigger it might be worth considering but for a 28 you've already got the right power.

Amen !! If you need to repower because the current 454s are flat worn-out, go back with new longblocks or semi-complete engines. Diesels would be a waste of your money. Man, you're doing 30kt @ 1 nmpg, I wish I had those numbers.