Power and drive systems for smaller planning hulls

What are your thoughts on diesel electric engines in a planning hull about 28' long? Ive always thought a diesel generator with two electric motors driving shafts would be interesting. I think the output needed to drive two electric motors would need a big generator. The boat we have is a 28 Bertram so room isnt something we have tons of.

I really like the benefits of the electrics but as with anything else powering them with any good output is the problem.

I wish some of the concept engines ive read about on here would have made it.

Another part of the system i was thinking about by reading various threads on here was the shaft. Om my size boat a pod just isnt practical, outboards dont handle well, waterjets would probably be similar to the outboards (if you could even get the RPM's so shaft driven props are really the solution. Ive read about the shaft sleeve to reduce drag and someone mentioning straightening out the shaft angle with a joint. I dont think th sleeve is going to be very beneficial but dont quite know how the 2 piece shaft would perform other than adding a failure point. What other options are there.

Another post i saw was about adding tunnels for the props. One poster said they had surface drives. Ive never driven or seen a boat in person with those. What performance effect do they have vs a conventional prop mounted on an angled shaft? I see they would have a draft and drag benefit but it seems like you would lose thrust. I saw one company making an internal pocket with the exhaust gasses blowing on the prop. According to them it was great of course but again it seems like you would lose thrust. What handling effect does changing that hull shape with either pockets or tunnels have?

The 28 bertram is more of a project or testbed to try out ideas and customise. Ill be doing most the work myself when i have time so materals are the only real cost. So any ideas or criticism are welcome. If nothing else id like to hear a general discussion on the topic even if its not related to the 28B.

Yep im sure your right on simplicity. I just like to play with ideas and see if anything beneficial can come out of it. If i had the money and time i would really like to design a boat from the ground up once i knew the theory side of it. That seems like it woul be a fun and interesting job.

A cruise of over 32 would be great but i dont know if that small of a Hp/Torque jump would gain that much. Ive looked into fitting a set of the Cummins 6BTA's in (mostly for cost over the yanmars) and they put out between 210 and 330 HP from what ive seen. I havent however been able to find out the details on how much room they really need for a good install.

From what ive read the 28's with the factry volvo diesels had a larger engine area and will fit them. I havnt been able to find a number on what the actual dimensions are though. My deck has already been raised to fit the Cummins 4BT's we have but they are just too underpowered to bother putting in i think. They are the 150 hp versions but have the fuel turned up and different injectors. So they should put out about 170 from what we are told.

I initially started on the prop pockets becuase we were looking into a 4 or 5 bladed prop to make things work right. By adding the pocket we may could stay with a 3 blade and depending on how i made them could level out the shaft some. A 31 Bertram i have some pictures of has the rudders and struts mounted at a slight angle from how it looks unless its just how the picture was taken. I cant find anything really on how they effect the handling or efficency of the boat.

It seems like it would almost give you more thrust but they have to be designed to allow the water to easily flow and fill the top of the pocket. Do any of you have any techinical documentation on the topic?

Thanks for the replies so far and pointing out as i thought diesel electric isnt practical for ths application.


EDITED TO ADD: What about the Volvo IPS system? That driven by a shaft would be a pretty interesting setup and would solve any clearance issues. I bet a pair of those cost a pretty penny. Have any of you used them or know what the cost per par is for the various models? That 4 cylinder would probably fit.